Treatment of heart disease by inhibition of the action of ribosomal s6 kinase 3 (rsk3)

ABSTRACT

The present invention provides a method of protecting the heart from damage, by administering to a patient at risk of such damage, a pharmaceutically effective amount of a composition which inhibits the interaction of RSK3 and mAKAPβ, or the expression or activity of one or both of those molecules. This composition may be in the form of a peptide that specifically inhibits mAKAPβ binding to RSK3 or in the form of an siRNA construct which inhibits the expression of RSK3.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 61/798,268, filed Mar. 15, 2013, which is hereby incorporated by reference in its entirety into the present application.

STATEMENT OF GOVERNMENTAL SUPPORT

This invention was made with Government support under contract RO1 HL 075398 awarded by the National Institutes of Health. The Government has certain rights in this invention.

BACKGROUND OF THE INVENTION

The heart is capable of undergoing hypertrophic growth in response to a variety of stimuli.

Hypertrophic growth may occur as the result of physical training such as running or swimming. However, it also occurs as the result of injury or in many forms of heart disease. Hypertrophy is the primary mechanism by which the heart reduces stress on the ventricular wall. When the growth is not accompanied by a concomitant increase in chamber size, this is called concentric hypertrophy. Hypertrophy occurs as the result of an increase in protein synthesis and in the size and organization of sarcomeres within individual myocytes. For a more thorough review of cardiac remodeling and hypertrophy, see Kehat (2010) and Hill (2008), each herein incorporated by reference in their entirety. The prevailing view is that cardiac hypertrophy plays a major role in heart failure. Traditional routes of treating heart failure include afterload reduction, blockage of beta-adrenergic receptors (β-ARs) and use of mechanical support devices in afflicted patients. However, the art is in need of additional mechanisms of preventing or treating cardiac hypertrophy.

AKAPs and Cardiac Hypertrophy

Ventricular myocyte hypertrophy is the primary compensatory mechanism whereby the myocardium reduces ventricular wall tension when submitted to stress because of myocardial infarction, hypertension, and congenital heart disease or neurohumoral activation. It is associated with a nonmitotic growth of cardiomyocytes, increased myofibrillar organization, and upregulation of specific subsets of “fetal” genes that are normally expressed during embryonic life (Frey 2004, Hill 2008). The concomitant aberrant cardiac contractility, Ca²⁺ handling, and myocardial energetics are associated with maladaptive changes that include interstitial fibrosis and cardiomyocyte death and increase the risk of developing heart failure and malignant arrhythmia (Cappola 2008, Hill 2008). Increased in prevalence by risk factors such as smoking and obesity, heart failure is a syndrome that affects about six million Americans and has an annual incidence of 1% of senior citizens (Roger 2011). Since the five-year survival rate after diagnosis is still very poor (lower than 50%), many efforts have been made during the last years to define the molecular mechanisms involved in this pathological process.

Cardiac hypertrophy can be induced by a variety of neuro-humoral, paracrine, and autocrine stimuli, which activate several receptor families including G protein-coupled receptors, cytokine receptors, and growth factor tyrosine kinase receptors (Brown 2006, Frey 2004). In this context, it is becoming increasingly clear that AKAPs can assemble multiprotein complexes that integrate hypertrophic pathways emanating from these receptors. In particular, recent studies have now identified anchoring proteins including mAKAP and AKAP-Lbc and D-AKAP1 that play a central role in organizing and modulating hypertrophic pathways activated by stress signals.

mAKAP.

In cardiomyocytes, mAKAPβ is localized to the nuclear envelope through an interaction with nesprin-1α (Pare 2007). mAKAPβ assembles a large signaling complex that integrates hypertrophic signals initiated by α1-adrenergic receptors (α1-ARs) and β-ARs, endothelin-1 receptors, and gp130/leukemia inhibitor factor receptors (FIG. 46A) (Dodge-Kafka 2005, Pare 2005). Over the last few years, the molecular mechanisms as well as the signaling pathways whereby mAKAPβ mediates cardiomyocyte hypertrophy have been extensively investigated. It is now demonstrated that mAKAPβ can recruit the phosphatase calcineurin Aβ (CaNAβ) as well as the hypertrophic transcription factor nuclear factor of activated T cells c3 (NFATc3) (Li 2010). In response to adrenergic receptor activation, anchored CaNAβ dephosphorylates and activates NFATc3, which promotes the transcription of hypertrophic genes (FIG. 46A) (Li 2010). The molecular mechanisms controlling the activation of the pool of CaNAβ bound to the mAKAPβ complex are currently not completely understood but seem to require mobilization of local Ca²⁺ stores. In this context, it has been shown that mAKAP favors PKA-induced phosphorylation of RyR2 (Kapiloff 2001), which, through the modulation of perinuclear Ca²⁺ release, could activate CaNAβ (FIG. 46A). In line with this hypothesis, the deletion of the PKA anchoring domain from mAKAPβ has been shown to suppress the mAKAP-mediated hypertrophic response (Pare 2005). On the other hand, recent findings indicate that mAKAPβ also binds phospholipase Cε(PLCε) and that disruption of endogenous mAKAPβ-PLCε complexes in rat neonatal ventricular myocytes inhibits endothelin 1-induced hypertrophy (Zhang 2011). This suggests that the anchoring of PLCε to the nuclear envelope by mAKAPβ controls hypertrophic remodeling. Therefore, it is also plausible that at the nuclear envelope, PLCε might promote the generation of inositol 1,4,5-trisphosphate, which through the mobilization of local Ca²⁺ stores, might promote the activation of CaNAβ and NFATc3 bound to mAKAPβ (FIG. 46A).

In cardiomyocytes, the dynamics of PKA activation within the mAKAP complex are tightly regulated by AC5 (Kapiloff 2009) and the PDE4D3 (Dodge-Kafka 2005, Dodge 2001) that are directly bound to the anchoring protein. The mAKAP-bound AC5 and upstream β-AR may be localized within transverse tubules adjacent to the nuclear envelope (Escobar 2011). In response to elevated cAMP levels, mAKAP-bound PKA phosphorylates both AC5 and PDE4D3 (Dodge-Kafka 2005, Dodge 2001, Kapiloff 2009). This induces AC5 deactivation and PDE4D3 activation, which locally decreases cAMP concentration and induces deactivation of anchored PKA (FIG. 46A). Dephosphorylation of PDE4D3 is mediated by the phosphatase PP2A that is also associated with mAKAPβ (FIG. 46A) (Dodge-Kafka 2010). Collectively, these findings suggest that the mAKAP complex generates cyclic pulses of PKA activity, a hypothesis that was supported experimentally by live cell imaging studies (Dodge-Kafka 2005).

AKAPs and Hypoxia

Myocardial oxygen levels need to be maintained within narrow levels to sustain cardiac function. During ischemic insult, in response to conditions of reduced oxygen supply (termed hypoxia), cardiomyocytes mobilize hypoxia-inducible factor 1α (HIF-1α), a transcription factor that promotes a wide range of cellular responses necessary to adapt to reduced oxygen (Semenza 2007). Transcriptional responses activated by HIF-1α control cell survival, oxygen transport, energy metabolism, and angiogenesis (Semenza 2007). Under normoxic conditions, HIF-1α is hydroxylated on two specific proline residues by the prolyl hydroxylase domain proteins (PHDs) and subsequently recognized and ubiquitinated by the von Hippel-Lindau protein (Jaakkola 2001, Maxwell 1999). Ubiquitinated HIF-1α is targeted to the proteasome for degradation. On the other hand, when oxygen concentration falls, the enzymatic activity of PHD proteins is inhibited. Moreover, PHD proteins are ubiquitinated by an E3 ligase named “seven in absentia homolog 2 (Siah2)” and targeted for proteasomal degradation (Nakayama 2004). This inhibits HIF-1α degradation and allows the protein to accumulate in the nucleus where it promotes gene transcription required for the adaptive re-sponse to hypoxia. In line with this finding, the delivery of exogenous HIF-1α improves heart function after myocardial infarction (Shyu 2002), whereas cardiac overexpression of HIF-1α reduces infarct size and favors the formation of capillaries (Kido 2005).

Recent findings indicate that mAKAP assembles a signaling complex containing HIF-1α, PHD, von Hippel-Lindau protein, and Siah2 (Wong 2008). This positions HIF-1α in proximity of its upstream regulators as well as to its site of action inside the nucleus. In this configuration, under normoxic conditions, negative regulators associated with the mAKAP complex favor HIF-1α degradation (Wong 2008). On the other hand, during hypoxia, the activation of Siah2 within the mAKAP complex promotes HIF-1α stabilization, allowing the transcription factor to induce transcription (Wong 2008). Therefore, mAKAP assembles a macromolecular complex that can favor degradation or stabilization of HIF-1α in cardiomyocytes in response to variations of oxygen concentrations. In this context, mAKAP could play an important role in cardiomyocyte protection during cardiac ischemia, when coronary blood flow is reduced or interrupted. By coordinating the molecular pathways that control HIF-1α stabilization in cardiomyocytes, mAKAP might favor HIF-1α-mediated transcriptional responses, controlling the induction of glycolysis (which maximizes ATP production under hypoxic conditions), the efficiency of mitochondrial respiration, and cell survival during ischemia (Semenza 2009).

Myofibrillar assembly driving nonmitotic growth of the cardiac myocyte is the major response of the heart to increased workload (Kehay 2010). Although myocyte hypertrophy per se may be compensatory, in diseases such as hypertension and myocardial infarction, activation of the hypertrophic signaling network also results in altered gene expression (“fetal”) and increased cellular apoptosis and interstitial fibrosis, such that left ventricular hypertrophy is a major risk factor for heart failure. Current therapy for pathologic hypertrophy is generally limited to the broad downregulation of signaling pathways through the inhibition of upstream cell membrane receptors and ion channels (McKinsey 2007). Novel drug targets may be revealed through the identification of signaling enzymes that regulate distinct pathways within the hypertrophic signaling network because of isoform specificity or association with unique multimolecular signaling complexes.

p90 ribosomal S6 kinases (RSK) are pleiotropic extracellular signal-regulated kinase (ERK) effectors with activity that is increased in myocytes by most hypertrophic stimuli (Anjum 2008, Sadoshima 2005, Kodama 2000). In addition, increased RSK activity has been detected in explanted hearts from patients with end-stage dilated cardiomyopathy (Takeishi 2002). There are 4 mammalian RSK family members that are ubiquitously expressed and that overlap in substrate specificity (Anjum 2008). RSKs are unusual in that they contain 2 catalytic domains, N-terminal kinase domain and C-terminal kinase domain (FIG. 4A, Anjum 2008). The N-terminal kinase domain phosphorylates RSK substrates and is activated by sequential phosphorylation of the C-terminal kinase domain and N-terminal kinase domain by ERK (ERK1, ERK2, or ERK5) and 3′-phosphoinositide-dependent kinase 1 (PDK1), respectively (Anjum 2008).

By binding scaffold proteins, RSKs may be differentially localized within subcellular compartments, conferring isoform-specific signaling bound to the scaffold protein muscle A-kinase anchoring protein (mAKAP) (Michael 2005). PDK1 activation of RSK was enhanced by co-expression with the mAKAP scaffold in a recombinant system. In cardiac myocytes, mAKAPβ (the alternatively spliced form expressed in muscle cells) organizes signalosomes that transduce cAMP, mitogen-activated protein kinase, Ca²⁺, and hypoxic signaling by binding a diverse set of enzymes, ion channels, and transcription factors (Kritzer 2012).

SUMMARY OF THE INVENTION

The following brief summary is not intended to include all features and aspects of the present invention, nor does it imply that the invention must include all features and aspects discussed in this summary.

The present inventors have discovered methods of treating cardiac pathological processes by inhibiting the signaling properties of individual mAKAP signaling complexes using drugs that target unique protein-protein interactions. Such a therapeutic strategy offers an advantage over classical therapeutic approaches because it allows the selective inhibition of defined cellular responses.

In particular, the present inventors have found that disrupting mAKAP-mediated protein-protein interactions can be used to inhibit the ability of mAKAP to coordinate the activation of enzymes that play a central role in activating key transcription factors that initiate the remodeling process leading to cardiac hypertrophy.

Specifically, the inventors have discovered that inhibiting the binding interaction between type 3 ribosomal S6 kinase (RSK3) and mAKAPβ can protect the heart from damage caused by various physical stresses, for example pressure overload and prolonged exposure to high levels of catecholamines.

Thus, the present invention comprises, in certain aspects a method for protecting the heart from damage, by administering to a patient at risk of such damage, a pharmaceutically effective amount of a composition which inhibits the interaction of RSK3 and mAKAPβ.

The invention also relates to a method of treating heart disease, by administering to a patient a pharmaceutically effective amount of a composition which inhibits the interaction of RSK3 and mAKAPβ.

The invention also relates to compositions which inhibit the interaction of RSK3 and mAKAPβ.

In still other embodiments, the inhibitors include any molecule that inhibits the expression or activity of RSK3 and mAKAPβ.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. Model for RSK3 signaling. MAP-Kinase signaling induced by α1-adrenergic receptor (α1-AR) stimulation and potentially other upstream signals activates anchored RSK3 in conjunction with PDK1 at anchored sites, including at perinuclear mAKAPβ signalosomes. Targets for RSK3 may include cytosolic and nuclear proteins, especially those involved in the regulation of hypertrophic gene expression.

FIG. 2. Shows the amino acid sequence of RSK3.

FIG. 3. Shows the amino acid sequence of mAKAPβ.

FIG. 4. The unique p90 ribosomal S6 kinase type 3 (RSK3) N-terminal domain binds muscle A-kinase anchoring protein (mAKAP). A, p90 ribosomal S6 kinases (RSKs) contain 2 catalytic domains, N-terminal kinase domain (NTKD) and C-terminal kinase terminal (CTKD).³ Only RSK3 has an N-terminal nuclear localization signal (NLS). This NLS is within the same unique region of RSK3 that binds mAKAPβ. In inactive RSK3, the CTKD binds the autoinhibitory domain (AID) α-helix. Prebound to the D-domain, when activated, extracellular signal-regulated kinase (ERK) phosphorylates RSK3 residues including the CTKD activation loop (T⁵⁷⁰). The CTKD then autophosphorylates S³⁷⁷, permitting phosphoinositide-dependent kinase 1 (PDK1) binding and phosphorylation of the NTKD activation loop (S²¹⁸). The NTKD phosphorylates RSK substrates. RSKs 1 to 4 were aligned and sequence similarity was calculated using Vector NTI AlignX (Invitrogen). RSK3 fragments used for mapping are indicated. B, Rat neonatal myocyte extract (lane 1, 0.2% total extract) was immunoprecipitated with preimmune (lane 2) or anti-VO56 mAKAP (lane 3) sera and detected using a pan-RSK antibody (C-20; see FIG. 21 legend). C, HA-tagged kinases and myc-tagged mAKAPα were expressed by cotransfection of HEK293 cells and coimmunoprecipitated with anti-HA antibody. D, HA-tagged RSK3 fragments and myc-tagged mAKAPβ were expressed by cotransfection of COS-7 cells and coimmunoprecipitated with anti-HA antibody. n≧3 for each panel.

FIG. 5. p90 ribosomal S6 kinase type 3 (RSK3) signaling is important for neonatal rat ventricular myocyte hypertrophy. A, Neonatal myocytes were infected with Adeno-HA-RSK3 for 1 day in maintenance media before being serum-starved for 2 days and then treated for 1 hour with 10 μmol/L phenylephrine (PE), 10 μmol/L BIX02189, or 0.1 μmol/L PD0325901. Whole cell extracts were used for immunoblotting (n=3). B-F, Myocytes were transfected with control or RSK3 siRNA oligonucleotides and cultured for 2 days±10% fetal bovine serum (FBS), 10 μmol/L PE, or 1000 U/mL leukemia inhibitory factor (LIF). B, RSK3 reverse-transcriptase polymerase chain reaction (RT-PCR; top) and Western blot for RSK3 immunoprecipitated with N-16 antibody (bottom) using PE-treated myocytes. C, Results obtained by TUNEL staining (n=3). D, Immunocytochemistry for α-actinin (green), atrial natriuretic factor (ANF; red), and Hoechst (blue); bar=20 μm. Separate ANF and Hoechst channels are provided in FIG. 23. E, Cross-section area of myocytes (n=4-8). F, Fraction of myocytes expressing ANF (n=4-5). *P values comparing samples treated with the same hypertrophic agonist. †P values compared with no hypertrophic agonist control.

FIG. 6. Inhibition of neonatal rat ventricular myocyte hypertrophy with p90 ribosomal S6 kinase (RSK) inhibitor. Myocytes were cultured for 2 days±10 μmol/L phenylephrine (PE), 1000 U/mL leukemia inhibitory factor (LIF), 10% fetal bovine serum (FBS), or 10 μmol/L BI-D1870 or 1% DMSO carrier. A, Immunocytochemistry for α-actinin (green), atrial natriuretic factor (ANF; red), and Hoechst (blue); bar=20 μm. Separate ANF and Hoechst channels are provided in FIG. 25. B, Cross-section area of myocytes (n=3-7). C, Fraction of myocytes expressing ANF (n=3). *P values compared with DMSO. †P values compared with no agonist control.

FIG. 7. The p90 ribosomal S6 kinase type 3 (RSK3) binding site within muscle A-kinase anchoring protein (mAKAP). A, mAKAP domain structure. Direct binding partners whose sites have been finely mapped in mAKAPβ are shown (Li 2010, Pare 2005, Zhang 2011, Dodge-kafka 2010, Kapiloff 2009, Kapiloff 1999, Marx 2001). mAKAPβ starts at residue 245 of mAKAPα. All fragments are numbered per mAKAPα. The grey bar indicates the RSK3 binding site. B-F, Specific tag antibodies were used to immunoprecipitate myc-tagged mAKAPβ and HA-tagged p90 ribosomal S6 kinase (RSK) proteins (see FIG. 4A) co-expressed in either HEK293 (B) or COS-7 (C-F) cells (n=3) for all panels. G, Surface plasmon resonance using purified bacterially expressed proteins. Unphosphorylated (left), extracellular-regulated signaling kinase (ERK)-phosphorylated (middle), and ERK and phosphoinositide-dependent kinase 1 (PDK1)-phosphorylated (right) His-RSK3 (12.5-200 nmol/L in perfusate) were bound to His-mAKAP 1286 to 1833 (solid state). Each curve was repeated 3 times using different protein preparations.

FIG. 8. p90 ribosomal S6 kinase type 3 (RSK3) anchoring is important for neonatal rat ventricular myocyte hypertrophy. A, Muscle A-kinase anchoring protein beta (mAKAPβ) complexes were immunoprecipitated using FL100 mAKAP antiserum from phenylephrine (PE)-treated, adenovirus-infected myocytes expressing myc-green fluorescent protein (GFP) or myc-GFP-mAKAP RSK binding domain (RBD) fusion protein (GFP-RBD; mAKAP 1694-1833) and detected with the pan-RSK 1F6 and mAKAP 211 antibodies. B, Transfected myocytes expressing GFP or GFP-RBD (green) were stained with α-actinin (blue) and atrial natriuretic factor (ANF; red) antibodies. Bar=20 μm. C, Cross-section area of myocytes (n=5). D, Fraction of myocytes expressing ANF (n=3). *P values comparing to GFP-expressing samples. †P values compared with no agonist control.

FIG. 9. p90 ribosomal S6 kinase type 3 (RSK3) knockout attenuates the effects of pressure overload in vivo. A, Hematoxylin and eosin-stained transverse sections. Bar=1 mm. B, Wheat-germ agglutinin-stained sections. Bar=50 μm. C, Cross-section area of myocytes in tissue sections (n=4-9). D, Bright field images of acutely dissociated adult cardiac myocytes. Bar=50 μm. Width (E), length (F), and length/width ratio (G) of isolated myocytes (n=5-6). †P values compared with sham-operated mice of the same genotype; *P values compared with RSK3^(+/+) transverse aortic constriction (TAC) mice.

FIG. 10 shows echocardiographic data for RSK^(−/−) mice after transverse aortic constriction.

FIG. 11 shows gene expression for RSK^(−/−) mice after transverse aortic constriction.

FIG. 12 shows breeding of RSK^(−/−) mice.

FIG. 13 shows echocardiographic data for RSK^(−/−) mice when unstressed.

FIG. 14 shows gravimetric data for RSK^(−/−) mice following TAC.

FIG. 15 shows echocardiographic data for RSK^(−/−) mice after isoproterenol infusion.

FIG. 16 shows gravimetric data for RSK^(−/−) mice after isoproterenol infusion.

FIG. 17 shows echocardiographic data for RSK^(−/−) mice after chronic exercise.

FIG. 18 shows gravimetric data for RSK^(−/−) mice after chronic exercise.

FIG. 19 shows sources of commercial antibodies used.

FIG. 20 shows sequences of oligonucleotides.

FIG. 21 Specificity of RSK3 Antibodies. A. HA-tagged RSK1, RSK2, RSK3 (in duplicate at different concentrations), RSK4, and MSK2 were expressed in COS-7 cells, and whole cell lysates were used for western blots with the indicated antibodies. B. Alignment of RSK and MSK family members. MSK1 and MSK2 are the only two other mammalian protein kinases that like RSK have a NTKD and a CTKD. When affinity purified, the OR43 antibody is highly selective for RSK3. The inventors did not test the Cell Signaling rabbit anti-RSK3 antibody #9343, since it is apparently RSK3-specific as shown by data provided by the manufacturer. The inventors also did not test the Santa Cruz goat anti-RSK3 antibody C-20 (sc-1431) used for immunoprecipitation of RSK3, since according to the manufacturer C-20 detects both RSK3 and to a lesser extent RSK2. The Santa Cruz goat anti-RSK3 antibody N-16 (sc-13378), also used for immunoprecipitation, is specific for RSK3 since the antigen was a peptide within the unique RSK3 N-terminus according to the manufacturer and as evident from our experiments. However, the monoclonal mouse anti-RSK3 antibody 1F6 (also sold as M01) sold by a variety of companies also readily detects RSK2. As might be expected from the conservation of the antigen sequence, the “RSK3” phospho-specific antibodies readily detected other RSK and MSK family members. Phosphorylation of S²¹⁸ was associated with a decreased mobility of most of the enzymes in SDS-PAGE, consistent with the multiple phosphorylation events that would be expected prior to PDK1 phosphorylation of that residue (Cf. FIGS. 22 and 5A). Note that the relatively increased detection of RSK4 with this antibody is consistent with RSK4 being constitutive active in cells.² Similarly, the relatively high signals for phospho-RSK3 are more likely attributable to an enhanced baseline ERK phosphorylation of RSK3 in cells than an increased specificity of this antibody for the RSK3 isoform.⁸ RSK3 is a minority of the total RSK protein in myocytes (see FIG. 24C). As a result, signal derived from endogenous proteins in whole cell lysates using these phospho-specific antibodies cannot be attributed solely to RSK3.

FIG. 22. RSK Activation in Neonatal Cardiac Myocytes. Neonatal rat ventricular myocytes were treated for 1 hour with 10 μmol/L PE, 10% FBS, or 1000 U/mL LIF in the absence or presence of the MAPK inhibitors as indicated. Total RSK was detected using the non-specific monoclonal RSK3 antibody 1F6 and the phospho-S²¹⁸ antibody. *p<0.05 relative to same condition without inhibitor; ††p<0.005 relative to control; n=2-7. Note that the graphs represent a compilation of the experiments presented in A and B, and therefore, the PE bars are the same in both graphs. PD0325901 is selective for MEK1/2 at 0.1 μmol/L, but also inhibits MEK5 at 10 μmol/L.⁹ BIX02189 is specific for MEK5. SP600125 and SB103580 are selective for JNK and p38, respectively.

FIG. 23 shows grayscale images of FIG. 5D

FIG. 24. Active RSK3 induces neonatal rat ventricular myocyte hypertrophy. Myocytes transfected with control or RSK3 siRNA oligonucleotides and infected with adenovirus to express GFP, HA-RSK3 or HA-RSK3 S²¹⁸A were cultured for 2 days±10 μmol/L PE. A. Immunocytochemistry for α-actinin (red) and Hoechst (blue); bar=20 μm. B. Cross-section area of myocytes. n=4-5. p<0.05: † compared to no agonist control; ‡, compared to control siRNA+GFP+PE; * compared to similarly treated GFP+RSK3 siRNA samples; § compared to similarly treated HA-RSK3 WT+RSK3 siRNA samples. C. Whole extracts and RSK3 immunoprecipitated with N-16 antibody were assayed by western blot. RSK3 in the immunoprecipitates and RSK in whole cell extracts were detected with purified OR43 and mouse 1F6 antibodies, respectively. Red asterisks indicate detectable endogenous and HA-tagged RSK3 proteins. Note that the signal obtained with both the phospho-S²¹⁸ and OR43 RSK3 antibodies were attenuated by the RSK3 siRNA and enhanced by HA-RSK3 expression. No signal was obtained for the HA-RSK3 S218A mutant with the phospho-S²¹⁸ antibody. The level of expression of HA-RSK3 in non-treated cells was similar to the level of expression of endogenous RSK3 in PE-treated cells. Importantly, neither expression of HA-tagged proteins, nor the use of the siRNA, affected the signal obtained using the pan-RSK antibody for whole cell extracts.

FIG. 25 shows grayscale images of FIG. 6A.

FIG. 26 shows Inhibition of neonatal rat ventricular myocyte hypertrophy with the RSK active site inhibitor SL0101. Myocytes were cultured for 2 days±10 μmol/L PE, 1000 U/mL LIF and/or 50 μmol/L SL0101 or 0.1% DMSO carrier. A. Immunocytochemistry for—actinin (red) and Hoechst (blue); bar=20 μm. B. Cross-section area of myocytes. n=5. † compared to no agonist control; * compared to no SL0101.

FIG. 27. Design of RSK3 Knock-out Mouse. A. A PGKneo cassette was inserted into Exon 2 interrupting translation at amino acid residue 67 within the ATP-binding cassette of the RSK3 NTKD. Fidelity of homologous recombination was confirmed using external probes for southern blotting and by PCR using the primers shown in black (sequence not shown). Prior to any experimentation, the PGKneo cassette was removed by mating targeted mice to a global cre transgenic mouse. PCR primers (red) used for genotyping were RSK3Ex2+5′ and RSK3Ex2-3′ that produce 336 and 421 bp fragments for wildtype and knock-out alleles, respectively. B. Example of mouse tail genotyping. C. Western blot of RSK3 proteins detected using OR43RSK3 antibody following immunoprecipitation by N-16 or C-20 antibodies. No RSK3 protein was detected in the knock-out mouse hearts. Western blot of whole heart extracts with the mouse 1F6 antibody (left panel) showed that despite the loss of RSK3 protein, total RSK detected in the knock-out hearts was the same as in wildtype.

FIG. 28. Echocardiography. Representative M-mode tracings for unstressed, sham-operated and TAC, saline and isoproterenol infused, and rested and swam mice. See FIGS. 10, 13, 15 and 16 for results.

FIG. 29. RSK3 is required for Isoproterenol-induced myocyte growth in width in vivo. A. Cross-section area of myocytes in tissue sections. n=3-5. Width (B), Length (C) and Length/Width Ratio (D) of acutely dissociated adult cardiac myocytes. n=5-6. †p-values comparing to untreated RSK3^(+/+) mice; ‡p-values comparing to saline-infused RSK3^(+/+) mice; * p-values comparing to Iso-infused RSK3^(+/+) mice.

FIG. 30. Phosphorylation of RSK3, ERK1/2, and known RSK substrates in mice hearts. 150 μg total heart extracts were analyzed by western blot for the indicated proteins for 2 weeks TAC (A) and isoproterenol infusion (B) cohorts. GSK-3βS⁹, myosin binding protein C (cMyBP-C) S²⁸², eukaryotic elongation factor-2 kinase (eEF2K) S³⁶⁶, and cardiac troponin I (TnI) S^(23/24) are known RSK substrates. Mouse IF6 RSK antibody was used to assay total RSK protein. No consistent changes in levels of total protein or phosphorylated proteins were detected.

FIG. 31 shows echocardiographic data for mice treated as in Example 2 at 16 weeks of age.

FIG. 32. TM180 C57BL/6; FVB/N mice have a small heart phenotype. A. Top panel: RSK3 protein was immunoprecipitated using N-16 antibody and detected using OR43 antibody. Middle panel: Total RSK protein in heart extracts was detected using mouse anti-RSK antibody. Bottom panel: Ponceau staining for total heart protein shows that the major α-TM wildtype band is replaced by a lower TM180 band in transgenic hearts (Prabhakar 2001). n=3 B. Biventricular weight indexed to tibial length. C. Wheat germ agglutinin-strained heart sections. Bar=50 μm. n=6 for each cohort. D. Wet lung weight indexed to tibial length. *p-values compared to WT cohort; †p-values compared to TM180 cohort. Cf. FIG. 34 for panels B and D.

FIG. 33. RSK3 is required for TM180 induced interstitial fibrosis. A. Trichrome staining of transverse sections. B. Higher magnification of trichrome stained section. Bar=100 μm. C. Picrosirius red staining of left ventricular sections and fibrillar collagen content quantified by linearly polarized light microscopy. Bar=200 μm. n=10-13; p(ANOVA)=0.002. D and E. Col8A1 (periostin) mRNA levels. n=3. Cf. FIG. 35. *p-values compared to WT cohort; †p-values compared to TM180 cohort.

FIG. 34 shows gravimetric data for mice treated as in Example 2.

FIG. 35 shows gene expression data from the method of Example 2.

FIG. 36 shows electrocardiography from the mice treated as in Example 2. A. Representative M-mode images for 16 week old mice. See FIG. 31 for values. B. Left ventricular internal diameter in diastole (LVID; d) for mice at the indicated ages by Mmode. C. Fractional shortening (%) by M-Mode for mice at the indicated ages. D. Endocardial Percent Fractional Area Change (Endocardial FAC) by B-Mode for mice at the indicated ages. * p-values when compared to WT; †p-values when compared to TM180. n=15-19 for each cohort. At all ages, the TM180 mice had significantly smaller internal LVID; d and significantly higher fractional shortening and Endocardial FAC than wildtype mice. At all ages, the TM180; RSK3−/−mice had mean values for these parameters that were closer to wildtype than those for the TM180 mice, albeit significance (p<0.05) between the TM180 and TM180; RSK3−/−mice cohorts was not reached for all of the age groups for each parameter.

FIG. 37 shows mAKAPβ as a scaffold for signaling molecules important for cardiac stress responses.

FIG. 38 shows the mAKAPβ signalosome.

FIG. 39 shows a conditional mAKAP (AKAP6) knock-out mouse allele.

FIG. 40 shows that mAKAPβ is important in the cardiac myocyte for the response to pressure overload.

FIG. 41 shows AAV2/9 transduced expression of anchoring disruptor peptides in vivo.

FIG. 42 shows results from a pilot study where mice were injected intraperitoneally as neonates and subjected to 2 week transverse aortic constriction (TAC) at 8 weeks of age.

FIG. 43 is the complete nucleotide and amino acid sequences of human RSK3. (Zhao et al. (1995) Mol. Cell. Biol. 1995, 15(8):4353.)

FIG. 44. Shows the nucleotide sequence of RSK3.

FIG. 45. Shows the nucleotide sequence of mAKAPβ.

FIG. 46. Regulation of cardiac hypertrophy by AKAP complexes. A: mAKAP assembles a multienzyme signaling complex at the outer nuclear membrane containing AC5, PKA, PDE4D3, PP2A, RyR2, calcineurin Aβ (CaNAβ), nuclear factor of activated T cells 3 (NFATc3), exchange protein activated by cAMP 1 (Epac1), and ERK5. Activation of AC5 by β-adrenergic stimulation generates cAMP, which in turn activates anchored PKA at submicromolar concentrations. In a negative feedback loop, activated PKA phosphorylates PDE4D3, leading to its activation and increased cAMP degradation, and AC5, leading to its inactivation and decreased cAMP synthesis. Anchored PKA also regulates the activity of PP2A, which promotes PDE4D3 dephosphorylation, and RyR2, which enhances Ca²⁺ mobilization from intracellular stores. This is proposed to induce the activation of CaNAβ, which, in turn, dephosphorylates and activates NFATc3 to promote hypertrophic gene transcription. Very high concentrations of cAMP (in μM) also stimulate Epac1. This in turn activates the GTPase Ras-related protein 1 (Rap1), which exerts an inhibitory effect on the MEK5-ERK5 pathway. In the absence of very high local cAMP, Epac1 is inactivated and the hypertrophic ERK5 pathway de-repressed. Stimulation of endothelin-1 receptors (ET1Rs) activates mAKAPβ-bound PLCε, which, in turn, promotes cardiomyocyte hypertrophy via a signaling pathway that remains to be elucidated. B: activated α₁-ARs and ET₁Rs stimulate the Rho-guanine nucleotide exchange factor (GEF) activity of AKAP-lymphoid blast crisis (AKAP-Lbc) through Gα₁₂. GTP-bound RhoA is released from the AKAP-Lbc complex and promotes cardiomyocyte hypertrophy via a signaling pathway that remains to be elucidated. Activation of AKAP-Lbc-anchored PKA promotes the phosphorylation of the anchoring protein on serine-1565. This induces the recruitment of 14-3-3, which inhibits the Rho-GEF activity of AKAP-Lbc. AKAP-Lbc also recruits PKCη and PKD. Upon stimulation by the Gα_(q)-phospholipase C pathway by α₁-ARs and ET₁Rs, PKCη becomes activated and phosphorylates PKD. Active PKD phosphorylates histone deacetylase 5 (HDAC5), causing its export from the nucleus. This favors myocyte-specific enhancer-binding factor 2 (MEF2)-dependent hypertrophic gene transcription. LIF-R, leukemia inhibitor factor receptor; IP3, inositol trisphosphate 1,4,5-trisphosphate.

DETAILED DESCRIPTION OF THE INVENTION

As discussed above, AKAP-based signaling complexes play a central role in regulating physiological and pathological cardiac events. As such, the present inventors have examined inhibiting the signaling properties of individual AKAP signaling complexes using drugs that target unique protein-protein interactions as an approach for limiting cardiac pathological processes. Such a therapeutic strategy offers an advantage over classical therapeutic approaches since it allows the selective inhibition of defined cellular responses.

Anchoring proteins including mAKAP are therapeutic targets for the treatment of cardiac hypertrophy and heart failure. In particular, the present inventors have found that disrupting AKAP-mediated protein-protein interactions can be used to inhibit the ability of mAKAP to coordinate the activation of enzymes that play a central role in activating key transcription factors that initiate the remodeling process leading to cardiac hypertrophy.

In particular, the inventors have found that type 3 ribosomal S6 kinase (RSK3) binds mAKAPβ directly via the unique N-terminal domain of RSK3, defining a novel enzyme-scaffold interaction. The inventors have found that anchored RSK3 regulates concentric cardiac myocyte growth, revealing an isoform-specific target for therapeutic intervention in pathologic cardiac hypertrophy. Delivery of such peptides that might inhibit RSK3-mAKAPβ interaction can be enhanced by the use of cell-penetrating sequences such as the transactivator of transcription peptide and polyarginine tails, or conjugation with lipid-derived groups such as stearate. Stability may also be enhanced by the use of peptidomimetics [i.e., peptides with structural modifications in the original sequence giving protection against exo- and endoproteases without affecting the structural and functional properties of the peptide. Alternatively, as shown in FIG. 41, peptides can be delivered by intracellular expression via viral-based gene therapy vectors.

The inventors have also found that small molecule disruptors can be used to target specific interaction within AKAP-based complexes. Small molecule disruptors can be identified by combining rational design and screening approaches. Such compounds can be designed to target-specific binding surfaces on AKAPs, to disrupt the interaction between AKAPs and PKA in cardiomyocytes and to enhance the contractility of intact hearts for the treatment of chronic heart failure.

The present invention relates to methods of treating any cardiac condition, which is initiated through the interaction of RSK3 and mAKAPβ. Such cardiac dysfunction can result in signs and symptoms such as shortness of breath and fatigue, and can have various causes, including, but not limited to hypertension, coronary artery disease, myocardial infarction, valvular disease, primary cardiomyopathy, congenital heart disease, arrhythmia, pulmonary disease, diabetes, anemia, hyperthyroidism and other systemic diseases.

In accordance with the present invention there may be employed conventional molecular biology, microbiology, and recombinant DNA techniques within the skill of the art. Such techniques are explained fully in the literature. See, e.g., Sambrook et al, “Molecular Cloning: A Laboratory Manual” (4th Ed., 2012); “Current Protocols in Molecular Biology” Volumes I-III [Ausubel, R. M., ed. (1994)]; “Cell Biology: A Laboratory Handbook” Volumes I-III [J. E. Celis, 3rd ed. (2005))]; “Current Protocols in Immunology” Volumes I-III [Coligan, J. E., ed. (2005)]; “Oligonucleotide Synthesis” (M. J. Gait ed. 1984); “Nucleic Acid Hybridization” [B. D. Hames & S. J. Higgins eds. (1985)]; “Transcription And Translation” [B. D. Hames & S. J. Higgins, eds. (1984)]; “Animal Cell Culture” [R. I. Freshney, ed. (1986)]; “Immobilized Cells And Enzymes” [IRL Press, (1986)]; B. Perbal, “A Practical Guide To Molecular Cloning” (1984); C. Machida, “Viral Vectors for Gene Therapy: Methods and Protocols” (2010); J. Reidhaar-Olson and C. Rondinone, “Therapeutic Applications of RNAi: Methods and Protocols” (2009).

The following definitions and acronyms are used herein:

ANF atrial natriuretic factor

CTKD C-terminal kinase domain

ERK extracellular signal-regulated kinase

FBS fetal bovine serum

GFP green fluorescent protein

Iso isoproterenol

LIF leukemia inhibitory factor

mAKAP muscle A-kinase anchoring protein

NTKD N-terminal kinase domain

PDK1 3′ phosphoinositide-dependent kinase 1

PE phenylephrine

RBD RSK binding domain

RSK p90 ribosomal S6 kinase

siRNA small interfering RNA oligonucleotide

TAC transverse aortic constriction

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described. Generally, nomenclatures utilized in connection with, and techniques of, cell and molecular biology and chemistry are those well known and commonly used in the art. Certain experimental techniques, not specifically defined, are generally performed according to conventional methods well known in the art and as described in various general and more specific references that are cited and discussed throughout the present specification. For purposes of the clarity, following terms are defined below.

The present invention recognizes that the interaction of RSK3 and mAKAPβ mediates various intracellular signals and pathways which lead to cardiac myocyte hypertrophy and/or dysfunction. As such, the present inventors have discovered various methods of inhibiting that interaction in order to prevent and/or treat cardiac myocyte hypertrophy and/or dysfunction.

Thus, the present invention includes a method for protecting the heart from damage, by administering to a patient at risk of such damage, a pharmaceutically effective amount of a composition, which inhibits the interaction of RSK3 and mAKAPβ. It should be appreciated that “a pharmaceutically effective amount” can be empirically determined based upon the method of delivery, and will vary according to the method of delivery.

The invention also relates to a method of treating heart disease, by administering to a patient a pharmaceutically effective amount of a composition, which inhibits the interaction of RSK3 and mAKAPβ.

The invention also relates to compositions which inhibit the interaction of RSK3 and mAKAPβ. In particular embodiments, these inhibiting compositions or “inhibitors” include peptide inhibitors, which can be administered by any known method, including by gene therapy delivery. In other embodiments, the inhibitors can be small molecule inhibitors.—

Specifically, the present invention is directed to methods and compositions for treating or protecting the heart from damage, by administering to a patient at risk of such damage, a pharmaceutically effective amount of a composition which (1) inhibits the interaction of RSK3 and mAKAPβ; (2) inhibits the activity of RSK3 and mAKAPβ; or (3) inhibits the expression of RSK3 and mAKAPβ.

The invention also relates to methods of treating or protecting the heart from damage, by administering to a patient at risk of such damage, a pharmaceutically effective amount of a composition which inhibits a cellular process mediated by the anchoring of RSK3 through its N-terminal domain.

In one embodiment, the composition includes an RSK3 peptide. In a preferred embodiment, the RSK3 peptide is obtained from the amino terminus of the RSK3 amino acid sequence. In a particularly preferred embodiment, the RSK3 peptide is amino acids 1-42 of the RSK3 amino acid sequence.

In another embodiment, the composition includes a small interfering RNA siRNA that inhibits the expression of either or both of RSK3 and mAKAPβ.

The composition of the invention can be administered directly or can be administered using a viral vector. In a preferred embodiment, the vector is adeno-associated virus (AAV).

In another embodiment, the composition includes a small molecule inhibitor. In preferred embodiments, the small molecule is SL0101 or BI-D1870.

In another embodiment, the composition includes a molecule that inhibits the binding, expression or activity of mAKAPβ. In a preferred embodiment, the molecule is a mAKAPβ peptide. The molecule may be expressed using a viral vector, including adeno-associated virus (AAV).

In yet another embodiment, the composition includes a molecule that interferes with RSK3-mediated cellular processes. In preferred embodiments, the molecule interferes with the anchoring of RSK3 through its N-terminal domain.

The invention also relates to diagnostic assays for determining a propensity for heart disease, wherein the binding interaction of RSK3 and mAKAPβ is measured, either directly, or by measuring a downstream effect of the binding of RSK3 and mAKAPβ. The invention also provides a test kit for such an assay.

In still other embodiments, the inhibitors include any molecule that inhibits the expression of RSK3 and mAKAPβ, including antisense RNA, ribozymes and small interfering RNA (siRNA).

The invention also includes an assay system for screening of potential drugs effective to inhibit the expression and/or binding of RSK3 and mAKAPβ. In one instance, the test drug could be administered to a cellular sample with the RSK3 and mAKAPβ, or an extract containing the RSK3 and mAKAPβ, to determine its effect upon the binding activity of the RSK3 and mAKAPβ, by comparison with a control. The invention also provides a test kit for such an assay.

In preparing the peptide compositions of the invention, all or part of the RSK3 (FIG. 2) or mAKAPβ (FIG. 3) amino acid sequence may be used. In one embodiment, the amino-terminal region of the RSK3 protein is used as an inhibitor. Preferably, at least 10 amino acids of the RSK3 amino terminus are used. More preferably, about 18 amino acids of the RSK3 amino terminus are used. Most preferably, amino acids from about 1-42 of the RSK3 amino terminus are used.

In other embodiments, at least 10 amino acids of the mAKAPβ sequence are used. More preferably, at least 25 amino acids of the mAKAPβ sequence are used. Most preferably, peptide segments from amino acids 1694-1833 of the RSK3 amino terminus are used.

It should be appreciated that various amino acid substitutions, deletions or insertions may also enhance the ability of the inhibiting peptide to inhibit the interaction of RSK3 and mAKAPβ. A substitution mutation of this sort can be made to change an amino acid in the resulting protein in a non-conservative manner (i.e., by changing the codon from an amino acid belonging to a grouping of amino acids having a particular size or characteristic to an amino acid belonging to another grouping) or in a conservative manner (i.e., by changing the codon from an amino acid belonging to a grouping of amino acids having a particular size or characteristic to an amino acid belonging to the same grouping). Such a conservative change generally leads to less change in the structure and function of the resulting protein. A non-conservative change is more likely to alter the structure, activity or function of the resulting protein. The present invention should be considered to include sequences containing conservative changes, which do not significantly alter the activity, or binding characteristics of the resulting protein.

The following is one example of various groupings of amino acids:

Amino Acids with Nonpolar R Groups:

Alanine, Valine, Leucine, Isoleucine, Proline, Phenylalanine, Tryptophan, Methionine.

Amino Acids with Uncharged Polar R Groups:

Glycine, Serine, Threonine, Cysteine, Tyrosine, Asparagine, Glutamine.

Amino Acids with Charged Polar R Groups

(negatively charged at pH 6.0): Aspartic acid, Glutamic acid.

Basic Amino Acids

(positively charged at pH 6.0): Lysine, Arginine, Histidine (at pH 6.0).

Another grouping may be those amino acids with phenyl groups: Phenylalanine, Tryptophan, Tyrosine.

Another grouping may be according to molecular weight (i.e., size of R groups): Glycine (75), Alanine (89), Serine (105), Proline (115), Valine (117), Threonine (119), Cysteine (121), Leucine (131), Isoleucine (131), Asparagine (132), Aspartic acid (133), Glutamine (146), Lysine (146), Glutamic acid (147), Methionine (149), Histidine (at pH 6.0) (155), Phenylalanine (165), Arginine (174), Tyrosine (181), Tryptophan (204).

Particularly preferred substitutions are:

-   -   Lys for Arg and vice versa such that a positive charge may be         maintained;     -   Glu for Asp and vice versa such that a negative charge may be         maintained;     -   Ser for Thr such that a free —OH can be maintained; and     -   Gln for Asn such that a free NH₂ can be maintained.

Amino acid substitutions may also be introduced to substitute an amino acid with a particularly preferable property. For example, a Cys may be introduced a potential site for disulfide bridges with another Cys. A His may be introduced as a particularly “catalytic” site (i.e., His can act as an acid or base and is the most common amino acid in biochemical catalysis). Pro may be introduced because of its particularly planar structure, which induces-turns in the protein's structure. Two amino acid sequences are “substantially homologous” when at least about 70% of the amino acid residues (preferably at least about 80%, and most preferably at least about 90 or 95%) are identical, or represent conservative substitutions.

Likewise, nucleotide sequences utilized in accordance with the invention can also be subjected to substitution, deletion or insertion. Where codons encoding a particular amino acid are degenerate, any codon which codes for a particular amino acid may be used. In addition, where it is desired to substitute one amino acid for another, one can modify the nucleotide sequence according to the known genetic code.

Two nucleotide sequences are “substantially homologous” when at least about 70% of the nucleotides (preferably at least about 80%, and most preferably at least about 90 or 95%) are identical.

The term “standard hybridization conditions” refers to salt and temperature conditions substantially equivalent to 5×SSC and 65 C for both hybridization and wash. However, one skilled in the art will appreciate that such “standard hybridization conditions” are dependent on particular conditions including the concentration of sodium and magnesium in the buffer, nucleotide sequence length and concentration, percent mismatch, percent formamide, and the like. Also important in the determination of “standard hybridization conditions” is whether the two sequences hybridizing are RNA-RNA, DNA-DNA or RNA-DNA. Such standard hybridization conditions are easily determined by one skilled in the art according to well known formulae, wherein hybridization is typically 10-20 C below the predicted or determined T_(m) with washes of higher stringency, if desired.

The phrase “pharmaceutically acceptable” refers to molecular entities and compositions that are physiologically tolerable and do not typically produce an allergic or similar untoward reaction, such as gastric upset, dizziness and the like, when administered to a human.

The phrase “therapeutically effective amount” is used herein to mean an amount sufficient to prevent, and preferably reduce by at least about 30 percent, more preferably by at least 50 percent, most preferably by at least 90 percent, a clinically significant change in a cardiac myocyte feature.

The preparation of therapeutic compositions which contain polypeptides, analogs or active fragments as active ingredients is well understood in the art. Typically, such compositions are prepared as injectables, either as liquid solutions or suspensions, however, solid forms suitable for solution in, or suspension in, liquid prior to injection can also be prepared. The preparation can also be emulsified. The active therapeutic ingredient is often mixed with excipients which are pharmaceutically acceptable and compatible with the active ingredient. Suitable excipients are, for example, water, saline, dextrose, glycerol, ethanol, or the like and combinations thereof. In addition, if desired, the composition can contain minor amounts of auxiliary substances such as wetting or emulsifying agents, pH buffering agents which enhance the effectiveness of the active ingredient.

A polypeptide, analog or active fragment, as well as a small molecule inhibitor, can be formulated into the therapeutic composition as neutralized pharmaceutically acceptable salt forms. Pharmaceutically acceptable salts include the acid addition salts (formed with the free amino groups of the polypeptide or antibody molecule) and which are formed with inorganic acids such as, for example, hydrochloric or phosphoric acids, or such organic acids as acetic, oxalic, tartaric, mandelic, and the like. Salts formed from the free carboxyl groups can also be derived from inorganic bases such as, for example, sodium, potassium, ammonium, calcium, or ferric hydroxides, and such organic bases as isopropylamine, trimethylamine, 2-ethylamino ethanol, histidine, procaine, and the like.

The therapeutic compositions of the invention are conventionally administered intravenously, as by injection of a unit dose, for example. The term “unit dose” when used in reference to a therapeutic composition of the present invention refers to physically discrete units suitable as unitary dosage for humans, each unit containing a predetermined quantity of active material calculated to produce the desired therapeutic effect in association with the required diluent; i.e., carrier, or vehicle.

The compositions are administered in a manner compatible with the dosage formulation, and in a therapeutically effective amount. The quantity to be administered depends on the subject to be treated, capacity of the subject's immune system to utilize the active ingredient, and degree of inhibition of RSK3-mAKAPβ binding desired. Precise amounts of active ingredient required to be administered depend on the judgment of the practitioner and are peculiar to each individual. However, suitable dosages may range from about 0.1 to 20, preferably about 0.5 to about 10, and more preferably one to several, milligrams of active ingredient per kilogram body weight of individual per day and depend on the route of administration. Suitable regimes for initial administration and booster shots are also variable, but are typified by an initial administration followed by repeated doses at one or more hour intervals by a subsequent injection or other administration. Alternatively, continuous intravenous infusion sufficient to maintain concentrations of ten nanomolar to ten micromolar in the blood are contemplated.

Because of the necessity for the inhibitor to reach the cytosol, a peptide in accordance with the invention may need to be modified in order to allow its transfer across cell membranes, or may need to be expressed by a vector which encodes the peptide inhibitor. Likewise, a nucleic acid inhibitor (including siRNAs and antisense RNAs) can be expressed by a vector. Any vector capable of entering the cells to be targeted may be used in accordance with the invention. In particular, viral vectors are able to “infect” the cell and express the desired RNA or peptide. Any viral vector capable of “infecting” the cell may be used. A particularly preferred viral vector is adeno-associated virus (AAV).

With respect to small molecule inhibitors, any small molecule that inhibits the interaction of RSK3 and mAKAPβ may be used. In addition, any small molecules that inhibit the activity of RSK3 and/or mAKAPβ may be used. Particularly preferred small molecules include BI-D1870, available from Enzo Life Sciences

and SL0101, available from Millipore:

Small molecules with similar structures and functionalities can likewise be determined by rational and screening approaches.

Likewise, any small molecules that inhibit the expression of RSK3 and/or mAKAPβ may be used.

In yet more detail, the present invention is described by the following items which represent preferred embodiments thereof:

-   -   1. A method of protecting the heart from damage, by         administering to a patient at risk of such damage, a         pharmaceutically effective amount of a composition which         inhibits the interaction of RSK3 and mAKAPβ.     -   2. The method of item 1, wherein the composition is a RSK3         peptide.     -   3. The method of item 2, wherein the RSK3 peptide is obtained         from the amino terminus of the RSK3 amino acid sequence.     -   4. The method of item 3, wherein the RSK3 peptide is amino acids         1-42 of the RSK3 amino acid sequence.     -   5. The method of item 2, wherein the polypeptide is administered         directly.     -   6. The method of item 2, wherein the polypeptide is administered         using a viral vector.     -   7. The method of item 6, wherein the vector is adeno-associated         virus (AAV).     -   8. The method of item 1, wherein the composition is a small         interfering RNA (siRNA) that inhibits the expression of RSK3.     -   9. A method of treating heart disease, by administering to a         patient a pharmaceutically effective amount of a composition         which inhibits the interaction of RSK3 and mAKAPβ.     -   10. The method of item 9, wherein the composition is a RSK3         peptide.     -   11. The method of item 10, wherein the RSK3 peptide is obtained         from the amino terminus of the RSK3 amino acid sequence.     -   12. The method of item 11, wherein the RSK3 peptide is amino         acids 1-42 of the RSK3 amino acid sequence.     -   13. The method of item 9, wherein the polypeptide is         administered directly.     -   14. The method of item 9, wherein the polypeptide is         administered using a viral vector.     -   15. The method of item 14, wherein the vector is         adeno-associated virus (AAV).     -   16. The method of item 19, wherein the composition is a small         interfering RNA (siRNA) that inhibits the expression of RSK3.     -   17. A composition comprising a molecule which inhibits the         interaction of RSK3 and mAKAPβ.     -   18. The composition of item 17, wherein the molecule is a         peptide.     -   19. The composition of item 18, wherein the molecule is a RSK3         peptide.     -   20. The composition of item 19, wherein the RSK3 peptide is         obtained from the amino terminus of the RSK3 amino acid         sequence.     -   21. The composition of item 20, wherein the RSK3 peptide is         amino acids 1-42 of the RSK3 amino acid sequence.     -   22. The composition of item 17, wherein the molecule is         expressed using a viral vector.     -   23. The composition of item 22, wherein the vector is         adeno-associated virus (AAV).     -   24. The composition of Item 17, wherein the molecule is a small         molecule.     -   25. A method of treating or preventing heart disease, by         administering to a patient a pharmaceutically effective amount         of a composition which inhibits the activity of RSK3.     -   26. The composition of item 25, wherein the small molecule is         SL0101 or BI-D1870.     -   27. A method of treating or preventing heart disease, by         administering to a patient a pharmaceutically effective amount         of a composition which inhibits the activity of mAKAPβ.     -   28. The method of item 27, wherein the composition is a mAKAPβ         peptide.     -   29. The composition of item 28, wherein the mAKAPβ peptide is         amino acids 1694-1833 of the mAKAPβ amino acid sequence.     -   30. The composition of item 28, wherein the mAKAPβ peptide is         amino acids 1735-1833 of the mAKAPβ amino acid sequence.     -   31. The composition of item 27, wherein the molecule is         expressed using a viral vector.     -   32. The composition of item 31, wherein the vector is         adeno-associated virus (AAV).

The following examples are provided to aid the understanding of the present invention, the true scope of which is set forth in the appended claims. It is understood that modifications can be made in the procedures set forth without departing from the spirit of the invention.

EXAMPLES

The compositions and processes of the present invention will be better understood in connection with the following examples, which are intended as an illustration only and not limiting of the scope of the invention. Various changes and modifications to the disclosed embodiments will be apparent to those skilled in the art and such changes and modifications including, without limitation, those relating to the processes, formulations and/or methods of the invention may be made without departing from the spirit of the invention and the scope of the appended claims.

Example 1 Methods

Reagents

Commercial antibodies and oligonucleotides are listed in FIG. 19 and FIG. 20. The commercially available RSK3 antibodies were of varying specificity (FIG. 21). Additional reagents and detailed methods are provided.

RSK3^(−/−) Mouse

All experiments involving animals were approved by the Institutional Animal Care and Use Committee at the University of Miami. Constitutive RSK3 knockout mice were backcrossed to C57BL/6 mice over 10 generations. All experiments were performed with littermate controls and mice that were 8 to 10 weeks of age at the beginning of the study. Transverse aortic constriction was performed as previously described (Rockman 1991), and isoproterenol infusion was via Alzet 2002 osmotic pumps (Durect). Echocardiography was performed under isoflurane anesthesia on a Vevo 770 High-Resolution Imaging System (VisualSonics).

RNA Assays

mRNA species were assayed using NanoString technology, a direct and multiplexed measurement of gene expression without amplification, using fluorescent molecular bar codes and single-molecule imaging to identify and count multiple transcripts in a single reaction; 100 ng of RNA was hybridized in solution to a target-specific code set overnight at 65° C., and individual mRNAs were counted using a NanoString Digital Analyzer.

Statistics

For all experiments, n refers to the number of individual mice or individual myocyte preparations. All data are expressed as mean±SEM. P values were calculated using Student t tests and are not corrected for multiple comparisons. Repeated symbols represent P values of different orders of magnitude (i.e., P<0.05, P<0.005, and others). All datasets involving multiple comparisons for which P values are provided also were significant by ANOVA (α=0.05).

Results

mAKAPβ: a Scaffold for RSK

The inventors have previously published that RSK proteins and activity are associated with mAKAPα complexes in the brain (Michel 2005). The inventors now show that RSK also is associated with mAKAPβ in cardiac myocytes (FIG. 4B). To determine whether mAKAP preferentially binds a specific RSK isoform, hemagglutinin (HA)-tagged RSK family members were co-expressed with mAKAP in HEK293 cells. In contrast to RSK1 and RSK2, RSK3 robustly mediated the coimmunoprecipitation of both mAKAPα and mAKAPβ (FIG. 4C). RSK family members are similar in primary sequence with the exception of the extreme N-terminal and C-terminal domains and a small region after the hydrophobic motif (FIG. 4A). Consistent with the selective binding of RSK3 to the scaffold, the N-terminal domain of RSK3 bound mAKAPβ (FIG. 4D).

RSK3 Function in Neonatal Cardiac Myocytes

RSK family members can be activated in most cell types by ERK, but not c-Jun N-terminal kinases or p38 (Anjum 2008). ERK phosphorylation is permissive for PDK1 phosphorylation of the RSK N-terminal kinase domain, such that PDK1 phosphorylation of RSK S²¹⁸ is indicative of full activation of the enzyme (FIG. 4A). To show that ERK activates RSK in cardiac myocytes, the inventors treated neonatal rat ventricular myocytes with different hypertrophic agonists and mitogen-activated protein kinase pathway inhibitors and detected RSK activation using a pan-RSK S²¹⁸ phosphor-specific antibody (FIGS. 21 and 22). The α-adrenergic stimulation with phenylephrine (PE) induced RSK phosphorylation 3-fold by both MEK1/2-dependent (that activates ERK1/2) and MEK5-dependent (that activates ERK5) mechanisms (FIG. 22). Moreover, MEK1/2 inhibition reduced RSK baseline phosphorylation. c-Jun N-terminal kinase and p38 inhibition did not affect PE activation and, in fact, variably increased baseline RSK phosphorylation. Fetal bovine serum and leukemia inhibitory factor also increased the level of activated RSK, but that occurred more so because of an increase in total RSK protein expression than because of ERK phosphorylation.

Similar results were found for HA-tagged RSK3 (FIG. 5A). Acute PE treatment induced the phosphorylation of HA-RSK3 ERK (S³⁶⁰) and PDK1 (S²¹⁸) sites through both MEK1/2-dependent and MEK5-dependent signaling. Together, these results confirmed that in cardiac myocytes ERK is responsible for RSK activation.

The inventors have previously demonstrated that mAKAPβ complexes are required for the hypertrophy of cultured myocytes (Li 2010, Pare 2005, Dodge-Kafka 2005). Therefore, the inventors proposed the hypothesis that RSK3 signaling is a major determinant of cardiac myocyte growth. Neonatal myocytes were transfected with small interfering RNA oligonucleotides (siRNA) that diminished RSK3 mRNA and protein levels by >75% (FIG. 5B). RSK3 siRNA did not induce the apoptosis of myocytes cultured either in the absence or in the presence of serum (FIG. 5C). Importantly, in the presence of α-adrenergic stimulation, RSK3 siRNA inhibited morphologic hypertrophy by 34% and atrial natriuretic factor expression completely (FIG. 5D-5F and FIG. 23). In addition, RSK3 siRNA had smaller, but detectable, effects on leukemia inhibitory factor and fetal bovine serum-stimulated hypertrophy. The results obtained by RSK3 RNA interference were confirmed with a second distinct RSK3 siRNA.

Endogenous RSK3 proteins are expressed at a relatively low level in cardiac myocytes compared with the other RSK family members and are induced in expression by long-term PE treatment (FIG. 24C). As a result, RSK3 RNA interference did not affect the level of total RSK in the myocyte, only diminishing the RSK3 detected after immunoprecipitation with a specific RSK3 antibody (FIG. 5B and FIG. 24C). In control experiments, the inhibition of PE-induced hypertrophy by the RSK3 siRNA was rescued by the expression of recombinant HA-tagged human RSK3, but not by an inactive HA-RSK3 S²¹⁸A mutant (FIGS. 24A and 24B). Remarkably, in these experiments, the cross-section area of unstimulated myocytes was increased by adenoviral-based expression of wild-type HA-RSK3 enzyme at a level comparable with that of endogenous RSK3 in PE-treated cells without affecting total RSK levels. Finally, to confirm that RSK activity was important for neonatal myocyte hypertrophy, the inventors used the pan-RSK inhibitors BI-D1870 (FIG. 6 and FIG. 25) and SL0101 (FIG. 26) (Smith 2005, Sapkota 2007, Malone 2005), finding that, like RSK3 siRNA, these compounds inhibited agonist-induced myocyte hypertrophy.

High-Affinity RSK3 Binding Domain in mAKAP

The inventors considered that the requirement for RSK3 in myocyte hypertrophy was attributable to the association of RSK3 with specific signaling complexes. To address this hypothesis, the inventors defined the mAKAP domains responsible for RSK3 binding. HA-tagged RSK3 was co-expressed in heterologous cells with myc-tagged mAKAPβ fragments and coimmunoprecipitated using a myc-tag antibody (FIGS. 7A and 7B). RSK3 preferentially associated with mAKAP amino acid residues 1286 to 1833, although it also weakly associated with mAKAP 245 to 587 and 525 to 1286. Consistent with this result, RSK3 binding to a full-length mAKAPβ protein with an internal deletion of residues 1257 to 1886 was reduced by >85%. Further mapping showed that the main RSK3 binding domain (RBD) of mAKAP mapped to a fragment encompassing residues 1694 to 1833 (FIG. 7C). Accordingly, RSK3 bound poorly to a full-length mAKAPβ protein with an internal deletion of residues 1701 to 1800 (FIG. 7D). As shown, the unique N-terminal domain of RSK3 bound full-length mAKAPβ (FIG. 4D). The mAKAP RBD also bound HA-RSK3 1 to 42 (FIG. 7E), but not to the N-terminally truncated RSK3 mutant (HA-RSK3 DN30) or the HA-tagged full-length RSK2 (FIG. 7F). These results imply that the mAKAP RBD is responsible for the selective binding of RSK3 to mAKAP.

The inventors next tested whether mAKAP-RSK3 binding is direct (FIG. 7G). The binding of bacterially expressed His-tagged mAKAP 1286 to 1833 and full-length RSK3 was analyzed by surface plasmon resonance. The binding was direct and of high affinity (nanomolar K_(D)). The inventors previously reported that once activated, RSK3 binds mAKAPα less well in cells (Michele 2005). Interestingly, previous RSK3 phosphorylation by either ERK or both ERK and PDK1 decreased the RSK3 binding affinity for mAKAP 5-fold and 8-fold, respectively, through a decrease in the association rate constant.

Disruption of RSK3 Anchoring Inhibits Neonatal Myocyte Hypertrophy

The identification of the high-affinity mAKAP RBD provided the opportunity to test whether anchoring of RSK3 is important for its function. When expressed in neonatal myocytes, a green fluorescent protein-mAKAP RBD fusion protein competed the association of endogenous RSK3 and mAKAPβ (FIG. 8A). Expression of green fluorescent protein-mAKAP RBD fusion protein markedly inhibited PE-induced hypertrophy (FIG. 8B-5D), similar to RSK3 siRNA (FIG. 5). Together, these results imply that RSK3 anchored to scaffolds through its unique N-terminal domain is required for the hypertrophy of cultured myocytes.

Role of RSK3 in Cardiac Hypertrophy In Vivo

The results obtained in vitro suggested that active RSK3 contributes to the development of pathologic myocyte hypertrophy. Further evidence supporting this hypothesis was obtained using a new RSK3 knockout mouse. By homologous recombination, stop codons were inserted into the second exon of the RSK3 (Rps6ka2) gene encoding the ATP-binding motif of the N-terminal kinase domain (Hanks 1988), resulting in the constitutive absence of RSK3 protein in homozygous null mice (FIG. 27). In general, RSK3^(−/−) mice appeared normal in morphology, were bred according to Mendelian genetics (FIG. 12), and exhibited no excess mortality up to 6 months of age. Before any stress, the RSK3^(−/−) mice had generally normal cardiac function, with the only measurable difference from wild-type littermates being a slight increase in left ventricular internal dimensions detected by echocardiography (FIGS. 13 and 28).

The inventors tested whether RSK3 is required for compensated cardiac hypertrophy by subjecting the RSK3^(−/−) mice to pressure overload for 2 weeks (FIG. 9A). By echocardiography, transverse aortic constriction (TAC) induced a 36% increase in posterior wall thickness in wild-type mice, but only a 16% increase in RSK3^(−/−) mice (FIGS. 10 and 28). The decreased hypertrophy was not accompanied by a change in contractility (fractional shortening). Postmortem gravimetric analysis showed that the corresponding increase in biventricular weight after TAC was similarly diminished in the knockout mice (48% for RSK3^(+/+) vs. 26% for RSK3^(−/−) mice; FIG. 14). TAC primarily induces concentric growth of cardiac myocytes.

Inspection of wheat germ agglutinin-stained heart sections revealed that consistent with these results, RSK3 knockout attenuated the TAC-induced increase in myocyte transverse cross-section area by ˜46% (FIGS. 9B and 9C). Proportional results were obtained by morphometric analysis of adult cardiac myocytes isolated from the TAC mice (FIG. 9D-9G).

To characterize the RSK3^(−/−) cardiac phenotype at a molecular level, the inventors surveyed for differences in the cardiac expression of 30 genes encoding proteins involved either in cardiac remodeling or in hypertrophic signaling (FIG. 11). Approximately two-thirds of the genes in our panel were significantly increased or decreased in expression by TAC. In general, the changes in expression were attenuated by RSK3 knockout. For example, TAC-induced atrial natriuretic factor expression was dramatically inhibited in RSK3^(−/−) mice, consistent with the results obtained for PE-treated neonatal myocytes. Although after 2 weeks of pressure overload the small increases in cellular apoptosis and interstitial fibrosis detectable by histology for wild-type mice did not reach significance when compared with sham-operated controls, these signs of remodeling tended to be less in the knockout mice (8.2±2.0 vs. 4.2±1.0×10⁻⁴ TUNEL-positive nuclei and 0.49%±0.18% vs. 0.29%±0.11% collagen staining for wild-type and RSK3^(−/−) TAC hearts, respectively). Interestingly, 2 genetic markers of fibrosis that were significantly induced in TAC wild-type mice, transforming growth factor β2 and collagen VI α1 (Yang 2012), were attenuated in expression by RSK3 knockout (FIG. 11).

To further explore the role of RSK3 in cardiac hypertrophy, the inventors used a second in vivo pathological stressor, chronic isoproterenol (Iso) infusion via subcutaneous osmotic pumps, and a physiological stressor, chronic exercise via swimming. Although Iso infusion resulted in a minor increase in ventricular wall thickness by echocardiography (FIG. 15), at the cellular level Iso significantly induced myocyte growth in width in a RSK3-dependent manner as measured by histology and after myocyte isolation (FIG. 29). Unlike TAC, Iso infusion also induced eccentric growth, as evidenced by increased myocyte length and ventricular dilation by echocardiography (FIGS. 15 and 16). This eccentric growth was not inhibited by RSK3 knockout. Together with the TAC data, these results demonstrate that RSK3 contributes to the induction of concentric myocyte hypertrophy in pathologic conditions.

Finally, RSK3^(−/−) mice were exercised by swimming. As expected (Perrino 2006), after swimming, wild-type mice exhibited a decreased resting heart rate (consistent with improved physical conditioning) and increased left ventricular internal dimensions (FIGS. 17 and 28). After exercise, there were no significant differences between RSK3 knockout and wild-type mice detectable by echocardiography, and the cohorts exhibited a similar increase in biventricular weight indexed by body weight (6% and 7%, respectively; FIG. 18).

Detailed Methods

Reagents:

Commercial antibodies are listed in FIG. 19. Secondary antibodies included horseradish peroxidase (HRP)-conjugated donkey secondary antibodies (Jackson ImmunoResearch) and Alexa dye-conjugated donkey secondary antibodies (Invitrogen). Monoclonal 211, polyclonal VO54, VO56 and OR010 mAKAP antibodies were as previously described and are available through Covance Research Products (Kehat 2010). OR42 and OR43 rabbit anti-RSK3 antisera were generated using bacterially-expressed His-tagged RSK3 (full-length) and affinity purified using antigen-coupled Affigel resin (Biorad). FL099 and FL100 rabbit anti-mAKAP antisera were generated using bacterially-expressed GST-tagged mAKAP 245-340. Oligonucleotides are listed in FIG. 20. Other reagents included: BIX02189—Boehringer Ingelheim Pharmaceuticals; PD0325901, SB103580, SL0101, and SP600125—EMD Chemicals Inc.

All adenovirus were constructed using the pTRE shuttle vector and the Adeno-X Tet-off System (Clontech) and purified after amplification using Vivapure AdenoPACK kits (Sartorius Stedim). These adenoviruses conditionally express recombinant protein when co-infected with tetracycline transactivator-expressing virus (adeno-tTA for “tet-off” or reverse tTA for “tet-on”). HA-tagged RSK and MSK2 expression plasmids acquired from Dario Alessi and John Blenis (McKinsey 2007, Anjum 2008, Sadoshima 1995) and myc-tagged mAKAP mammalian expression vectors (pcDNA3.1 (−) myc-his) and adenovirus were as previously described (Kodama 2000, Takeishi 2002). GFP-RBD was expressed using a pEGFP-based plasmid. Bacterial expression vectors for mAKAP and RSK3 were constructed using pET30 and pGEX-4T parent vectors, and proteins were purified using His-bind (Novagen) and Glutathione Uniflow Resins (Clontech).

Neonatal Rat Myocytes Isolation and Culture:

1-3 day old Sprague-Dawley rats were decapitated and the excised hearts placed in 1×ADS Buffer (116 mmol/L NaCl, 20 mmol/L HEPES, 1 mmol/L NaH₂PO₄, 5.5 mmol/L glucose, 5.4 mmol/L KCl, 0.8 mmol/L MgSO₄, pH 7.35). The atria were carefully removed and the blood washed away. The ventricles were minced and incubated with 15 mL 1×ADS Buffer containing 3.3 mg type II collagenase (Worthington, 230 U/mg) and 9 mg Pancreatin (Sigma) at 37° C. while shaking at 80 RPM. After 15 minutes, the dissociated cardiac myocytes were separated by centrifugation at 50×g for 1 minute, resuspended in 4 mL horse serum and incubated 37° C. with occasional agitation. The steps for enzymatic digestion and isolation of myocytes were repeated 10-12 times to maximize yield. The myocytes were pooled and spun down again at 50×g for 2 minutes and resuspended in Maintenance Medium (DMEM:M199, 4:1) supplemented with 10% horse serum and 5% fetal bovine serum. To remove any contaminating fibroblasts, the cells were pre-plated for 1 hour before plating on gelatin-coated tissue culture plasticware. This procedure yields >90% pure cardiac myocytes. After 1 day in culture, the media was changed to maintenance medium containing 0.1 mmol/L bromodeoxyuridine to suppress fibroblast growth.

Experiments were initiated 1 day after myocyte isolation. Adenoviral infection was performed by addition of adenovirus (multiplicity of infection=5-50) to the media. Plasmids and siRNA oligonucleotides were transfected using Transfast (Promega) and Dharmafect (Thermofisher), respectively, as recommended by the manufacturers using cells cultured in maintenance medium supplemented with 4% horse serum. Starting the day after gene transduction, the cells were treated for as long as 2 days, as indicated for each experiment.

Immunoprecipitations:

HEK293 and COS-7 cells were transfected with Lipofectamine 2000 (Invitrogen) or Polyethylenimine “Max” (Polysciences). Cells (including myocytes) were lysed in buffer (20 mmol/L HEPES, pH 7.4, 150 mmol/L NaCl, 5 mmol/L EDTA, 0.5% Triton, 50 mmol/L NaF, 1 mmol/L sodium orthovanadate, 1 mmol/L DTT, and protease inhibitors). After centrifugation at 10,000×g for 10 minutes at 4° C., the clarified extracts were used for immunoprecipitation using appropriate antibodies (10 μg purified antibody or 1-5 μL whole serum) and 20 μL protein G sepharose (Millipore, Fastflow) for 3 hours to overnight at 4° C. The beads were washed 3-5 times with lysis buffer, and the immunoprecipitated proteins were eluted with 1× Laemmli buffer for western blotting. Western blots were developed using horseradish peroxidase-conjugated donkey secondary antibodies, Supersignal West Chemiluminescent Substrates (Thermo Scientific) and X-ray film or a Fujifilm LAS-3000 imaging system.

Immunocytochemistry:

Cultured neonatal cardiomyocytes on plastic coverslips were fixed in 3.7% formaldehyde in PBS, permeabilized with 0.3% Triton X-100 in PBS, and blocked with PBS containing 0.2% BSA and 1% horse serum for 1 hour. The slides were then sequentially incubated for 1 hour with primary and Alexa fluorescent dye-conjugated specific-secondary antibodies (Invitrogen, 1:1000) diluted in blocking buffer. The slips were washed three times with blocking buffer. 1 μg/mL Hoechst 33258 was included in the last wash stop to label nuclei. Slides were sealed in SlowFade Gold antifade buffer (Invitrogen) for fluorescent microscopy. Wide-field images were acquired using a Leica DMI 6000 Microscope.

Surface Plasmon Resonance:

SPR analysis was performed using a BIAcore T100. 200 resonance units His-tagged mAKAP 1286-1833 were covalently immobilized using NHS (N-hydroxysuccinamide) and EDC [1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide] (Biacore amine coupling kit) to the surface of a sensor chip (BIAcore type CM5). His-RSK3 analytes (6.25-200 nmol/L) in HBS buffer (10 mmol/L Hepes, pH 7.4, 150 mmol/L NaCl, and 0.005% Surfactant P20) were injected at a flow rate of 30 μL/min for 5 minutes, followed by buffer alone for another 5 minutes. Sensorgrams were processed by BIAcore T100 evaluation software.

For phosphorylated His-RSK3, 20 μg His-RSK3 was phosphorylated with 2 μg ERK2 (Millipore, 14-550) and/or PDK1 (Sigma, P7498) for 5 hours in kinase buffer (20 mmol/L MOPS, pH 7.2, 25 mmol/L β-glycerol phosphate, 5 mmol/L EGTA, 1 mmol/L sodium orthovanadate, 1 mmol/L DTT) with 0.5 mmol/L MgATP. Phospho-His-RSK3 was purified using His-binding beads and concentrated before use.

Generation of RSK3^(−/−) Mouse:

All experiments involving animals were approved by the Institutional Animal Care and Use Committee at the University of Miami. Constitutive knock-out mice were generated using a targeting vector that inserted into Exon 2 a neomycin resistance gene (PGKneo) flanked by loxp sites (FIG. 27). Targeted 129SvJ ES cells were injected into C57BL/6J blastocysts. PGKneo was removed by crossing mutant mice with B6.C-Tg(CMV-cre)1Cgn/J (The Jackson Laboratory). RSK^(+/−) Mice were selected for loss of the cre transgene and backcrossed to C57BL/6 mice over 10 generations. All experiments were performed with littermate controls and mice that were 8-12 weeks of age. The numbers of mice in each cohort are listed in the various tables and figures.

Isoproterenol Infusion:

Alzet 2002 osmotic pumps (Durect) were sterilely loaded with 200 μL saline or saline and isoproterenol to deliver 60 mg/kg/day for 14 days. 8 week old mice were anaesthetized, and the pump was inserted sterilely subcutaneously into the shaved back through a transverse incision made intra-scapulae. The wound was closed with surgical staples and covered with betadine solution. Mice were housed separately after surgery.

Transverse Aortic Constriction:

All tools were sterilized with a Germinator 500 Dry Sterilizer and Betadine Solution (10% povidone-iodine topical solution). Anesthesia was induced with 5% isoflurane and maintained with 2% isoflurane and 100% oxygen at a flow rate of 1.5 L/min using a SurgiVet flow regulator via nose cone. Loss of consciousness was verified by toe pinch. Mouse fur over the left chest and sternum was removed with a calcium hydroxide lotion (e.g. Nair), and the surgical site was sterilized with betadine. The skin was incised exposing the pectoralis muscle and the second left intercostal space. The pectoralis muscle and the second rib were blunt dissected and retracted revealing the thymus within the mediastinum. The lobes of the thymus were retracted to reveal the transverse aortic arch as well as the right innominate and left common carotid arteries. Blunt dissection though the connective tissue between these two arteries and under the aorta allowed for the passage of a 6-0 silk using a modified ligation aid (Fine Science Tools 18062-12). A 27 gauge needle was placed on top of the aorta and the 6-0 silk was tied around the needle. The needle was removed, leaving a constricted aorta. The chest was closed in two layers with 5-0 Polysorb Suture. Isoflurane administration was terminated, and the mice were maintained on 100% oxygen by nose cone until conscious. Immediately post-operatively, buprenorphrine (0.05-0.1 mg/kg s.c.) was administered and then q12 h prn. The mice were allowed to recover under a heat lamp until alert and active. Sham-operated mice that experience all but the placement of the aortic ligature served as controls.

Swimming:

8-10 week old mice were forced to swim in water tanks every day for 4 weeks. The swimming tank measured >225 cm², with a depth of 15 cm and a water temperature of 30-32° C. Mice were continuously observed to avoid any drowning. The first day of training consisted of two 10-min sessions separated by at least 4 h. Sessions were increased by 10 min each day until 90-min sessions were reached. Additional cohorts were housed normally without exercise to serve as a “sham swim” control group. Food and water were provided ad libitum throughout the month period for all mice.

Echocardiography:

Mice minimally anesthetized with 1-2% isoflurane were studied using a Vevo 770®, High-Resolution Imaging System (VisualSonics). The pressure gradient following TAC was calculated from the pulse wave Doppler velocity at the point of ligation as follows: P=4ν²; P=the induced pressure gradient (in mmHg) and ν=the velocity across the constriction (in m/s).⁷

Adult Mouse Myocytes Isolation by Langendorff Perfusion:

Mice were anesthetized using Ketamine (80-100 mg/kg) and Xylazine (5-10 mg/kg) IP followed by 200 U heparin IP and cardiac excision. The heart was placed immediately in perfusion buffer (NaCl 120 mmol/L, KCl 5.4 mmol/L, Na₂HPO₄.7H₂O 1.2 mmol/L, NaHCO₃ 20.0 mmol/L, MgCl₂.6H₂O 1.6 mmol/L, Taurine 5 mmol/L, Glucose 5.6 mmol/L) equilibrated with 95% O₂ and 5% CO₂. The heart was attached via the aorta to the condenser outlet of a Harvard Langendorff apparatus. Ca²⁺-free perfusion lasted for 5 minutes with a constant rate at 2.2 mL/min at 37° C. The heart was digested by continuous perfusion with 25 mL buffer containing 25 mg type II collagenase (Worthington, 315 U/mg) and 1.3 mg protease (Sigma type XIV). After removal of the atria, the ventricles were then immersed in 5 mL of the same enzyme solution for dissociation by cutting into small pieces and by passing through a large bore pipette. The cell slurry was filtered through a 150-200 μm nylon mesh and the myocytes relaxed by incubation for 10 minutes in perfusion buffer containing 10 mmol/L KCl. The cells were fixed in suspension in perfusion buffer containing 3.7% formaldehyde, before morphometric analysis by light microscopy.

Histochemistry:

Heart tissue was fixed in 3.7% formaldehyde. De-paraffinized 5 μm tissue sections were stained using the Picrosirius Red Stain Kit (Polysciences) and Alexa Fluor 555 Wheat Germ Agglutinin conjugate (Invitrogen) as recommended by the manufacturers. The cross-section area of >150 myocytes in >3 distinct regions of the left ventricle were measured per heart using the wheat germ agglutinin sections. Collagen content was assayed using the Picrosirius Red stained sections and polarized light microscopy for >3 5× objective fields per heart. TUNEL staining for both fixed cells and tissue sections was performed using the In Situ Cell Death Detection Kit, TMR red (Roche). Morphometrics and collagen content were measured using IPLab microscope software (BD Biosciences).

Morphometry:

Morphometric data was acquired using IPLab Software. For neonatal myocytes, at least 6 separate images, each containing >100 cells, were assayed for cross-section area and perinuclear prepro-ANF staining per condition for each repetition of the experiment. For adult mouse cardiac myocytes, the maximum lengths perpendicular (width) or parallel (length) to the myofibrils were measured for >100 freshly dissociated myocytes per heart.

RNA Assays:

Total RNA was quantified with a Nanodrop 8000 Spectrophotometer (Thermo Scientific) and quality controlled using with a Bioanalyzer 2100 and the RNA 6000 Nano kit (Agilent). qRT-PCR was performed using SYBR green.

The NanoString assay is based on direct, multiplexed measurement of gene expression without amplification, utilizing fluorescent molecular barcodes and single molecule imaging to identify and count multiple transcripts in a single reaction. For Nanostring assay, 100 ng total RNA were hybridized in solution to a target-specific codeset overnight at 65° C. The codeset contained dual, adjacently placed 50 bp oligonucleotide probes against a panel of 30 genes, one set of probes fluorescently bar-coded and the other biotinylated. The hybridization reactions were loaded onto the NanoString Prep station which removes excess oligonucleotides and binds the hybridized mRNA to the Streptavidin-coated cartridge surface. The cartridges were loaded onto the NanoString Digital Analyzer, and 1155 fields of view were fluorescently scanned to count only those individual mRNAs bound to both a biotinylated and fluorescently bar-coded probe. Datasets for each RNA sample were background-subtracted and normalized using Gapdh. In validation assays, NanoString counts were directly proportional over 3 orders of magnitude to the mRNA levels obtained by qRT-PCR and had a similar minimum level of detection.

Statistics:

For all experiments, n refers to the number of individual mice or individual myocyte preparations. All data are expressed as mean±s.e.m. p-values were calculated using two-tailed Student's t-tests, paired or un-paired as appropriate, and are not corrected for multiple comparisons. Repeated symbols represent p-values of different orders of magnitude, for example: * p<0.05, ** p<0.005, *** p<0.0005, etc. All datasets involving multiple comparisons for which p-values are provided were also significant by ANOVA, α0.05.

Discussion

RSK activity is associated with the function of the nervous system, immunity, muscle, and cancer (Anjum 2008). Human RSK2 mutations cause X-linked Coffin-Lowry syndrome, which includes mental and growth retardation and skeletal and facial anomalies, but rare cardiac abnormality. In the heart, RSK1 and RSK2 can activate the Na⁺/H⁺ exchanger NHE1, and α-adrenergic-induced NHE1 phosphorylation is blocked by fmk, which inhibits all RSKs except RSK3 (Cuello 2007). The inventors now reveal a role for RSK3 in the cardiovascular system, regulation of pathological myocyte hypertrophy.

Cardiac myocytes can grow in both width and length, termed concentric and eccentric hypertrophy, respectively (Kehat 2010). Concentric myocyte hypertrophy involves the parallel assembly of contractile units (sarcomeres), increasing potential myocyte tension and wall thickness. In contrast, eccentric myocyte hypertrophy involves the serial assembly of sarcomeres along the axis of contraction, mainly contributing to increased ventricular wall area. The inventors found that RSK3 was required for TAC-induced concentric hypertrophy, as well as for Iso-induced myocyte growth in width in vivo. These differences can be modeled in vitro. Interleukin-6 cytokines such as leukemia inhibitory factor and cardiotrophin-1 induce an elongated and eccentric phenotype for cultured neonatal myocytes, in contrast to the symmetric growth stimulated by PE (Wollert 1996). Interestingly, the growth of the cultured myocytes tended to depend on RSK3 more when induced by α-adrenergic stimulation than by leukemia inhibitory factor (FIGS. 5 and 6). The greater inhibition of PE-induced morphologic hypertrophy was consistent with the more robust activation of RSK by PE than leukemia inhibitory factor (FIG. 22), as well as the results obtained in vivo.

RSK3 was activated in myocytes by ERK1, ERK2, and ERK5 (FIG. 5A). Whereas RSK3 has been absent from the cardiac literature, ERK signaling has been well-studied both in human disease and in animal models. The autosomal-dominant human syndromes Noonan, Costello, cardiofaciocutaneous, and LEOPARD result from mutations in PTPN11, HRAS, RAF1, BRAF, MEK1, and MEK2 that activate ERK1/2 signaling (Wu 2011). These Rasopathies feature developmental delay, dysmorphic features, and defects in multiple organ systems, often including a hypertrophic phenotype Gelb 2011). In mice, left ventricular hypertrophy has been induced by cardiac myocyte-specific expression of constitutively active H-Ras and MEK1, as well as cardiac-specific deletion of the Ras GTPase-activating protein neurofibromin that inhibits Ras signaling (Rose 2010, Xu 2009). Conversely, transgenic expression of dominant-negative Raf1 inhibited the hypertrophy due to pressure overload.

Recently, investigators have shown that cardiac myocyte-specific knockout of all 4 ERK1/2 alleles resulted in a severe, fatal dilated cardiomyopathy without increased myocyte death (Kehat 2011). ERK1/2-null myocytes were longer and narrower than those from control animals. PTPN11 (Shp2) knockout that decreased ERK1/2 activation also resulted in an elongated myocyte morphology and dilated cardiomyopathy (Kontaridis 2008).

Conversely, myocytes from constitutively active MEK1 transgenic mice were shorter and wider (Kehat 2011). In contrast to the ERK1/2 and Shp2 knockout mice, the inventors found that deletion of the down-stream effector RSK3 resulted in a milder phenotype, with the defect in concentric growth significant only after TAC and Iso infusion. Together, these observations are consistent with the hypothesis that ERK1/2 signaling through RSK3 promotes stress-induced concentric growth of cardiac myocytes independently of other signaling pathways that regulate eccentric hypertrophy.

The inventors found that RSK3 was activated in myocytes by not only ERK1/2 but also ERK5. There is evidence that MEK5-ERK5 signaling primarily induces eccentric myocyte hypertrophy (Nicol 2001), although ERK5 also may contribute to concentric growth (Kimura 2010).

The data obtained using the RSK knockout mouse establish a function for RSK3 in pathological remodeling. Without being bound by any particular theory, it is also possible that RSK3 has a role in physiologic hypertrophy. For example, the myocytes isolated from unstressed RSK3^(−/−) mice tended to be smaller in both width and length (FIGS. 9 and 29). In addition, after swimming, RSK3^(−/−) biventricular weight was less than that of wild-type mice, albeit not significantly after normalization by body weight (FIG. 18).

It is remarkable that even though RSK3 constitutes a minority of the total RSK in the myocyte (FIGS. 24 and 30), RSK3 activity is, nevertheless, required for myocyte growth. The differential anchoring of RSK3 by scaffold proteins provides a mechanism by which RSK3 may specifically function in vivo. Scaffolds are likely to be most important for enzymes such as RSK3 that are low in abundance and that have broad intrinsic substrate specificity. RSK protein kinases catalyze the phosphorylation of RxRxx(S/T) sites and overlap in specificity with other AGC kinases (Anjum 2008). By co-localizing enzymes, their upstream activators, and substrate effectors, scaffolds can accelerate the kinetics of signaling, amplify responses, increase specificity in enzyme catalysis, and direct signaling to specific subcellular compartments (Good 2011). The prior art provides limited guidance with respect to RSK compartmentation in cells or participation in multi-molecular signaling complexes. On mitogen stimulation, cytosolic RSK1 (and potentially other RSK isoenzymes) can transiently translocate to the plasma membrane, whereas activated RSK tends to be enriched in the nucleus (Anjum 2008). In neurons, RSKs bind PDZ domain-containing proteins via their conserved C-terminal STxL peptides, directing the kinases to substrates involved in synaptic transmission (Thomas 2005). By another mechanism, RSK1 binds type 1 protein kinase A and D-AKAP-1, a mitochondrion-localized scaffold (Chaturvedi 2006, Huang 1997). Consistent with the fact that the inventors can only detect RSK3 in myocytes after immunoprecipitation, the inventors have not been able to detect endogenous RSK3 protein by immunocytochemistry. When overexpressed at a low level, HA-RSK3 was enriched at the nuclear envelope, the predominant location for mAKAPβ in the cardiac myocyte (Pare 2005). By characterizing in detail the protein-protein interaction between the unique RSK3 N terminus and mAKAPβ, the inventors have identified a new mechanism by which RSK3 can be specifically anchored by ≧1 scaffolds that may be targeted to different signaling compartments.

The inventors demonstrated the functional significance of this RSK3 anchoring using a competing binding peptide (mAKAP RBD) that inhibited myocyte hypertrophy.

The regulation of NHE1 by RSK1/2 has spurred recent interest in using RSK inhibitors to treat heart disease (Avkiram 2008). The inventors show that RSK3 knockout reduced TAC-induced hypertrophy without diminishing cardiac function and while inhibiting the expression of genetic markers for pathological remodeling. RSK inhibition may have multiple applications, including its use in acquired diseases such as hypertension (pressure overload) and for the treatment of the aforementioned Rasopathies. Recently, a Noonan syndrome mouse model (Raf1L⁶¹³V knock-in) mouse was treated with PD0325901, resulting in the attenuated progression of cardiac hypertrophy cardiomyopathy and other Noonan characteristics (Wu 2011). Targeting of RSK3 offers an alternative approach to avoid some of the harmful side effects of global ERK pathway inhibition. The use of RSK3 inhibitors that either competitively bind the active site or disrupt anchoring are offered as novel cardiac therapies.

Example 2

Remodeling of the extracellular matrix and the induction of myocardial interstitial fibrosis is an important factor contributing to the development of heart failure in cardiac disease (Spinale 2013, Edgley 2012). Increased deposition of fibrillar collagen and disruption of the normal cellular architecture of the myocardium can result in decreased compliance and both diastolic and systolic dysfunction, as well as arrhythmia due to interference with the electrical conduction system. p90 ribosomal S6 kinases (RSK) are pleiotropic protein kinases that are activated in myocytes in response to many stress-related stimuli (Anjum 2008, Sadoshima 2005, Kodama 2000). The inventors have shown that type 3 RSK (RSK3) is required for the induction of concentric myocyte hypertrophy in mice subjected to pressure overload (Li 2013). Activated by sequential phosphorylation by extracellular signal-regulated kinases (ERKs) and 3′-phosphoinositide-dependent kinase 1, RSK3 is one of four RSK family members expressed in the heart (Anjum 2008). Remarkably, even though RSK3 comprises a minority of RSK enzyme in cardiac myocytes, RSK3 is required for hypertrophy (Li 2013). Due to its role in pathological hypertrophy, the inventors have suggested that RSK3 targeting might be beneficial in the prevention of heart failure. To our knowledge, however, the prior art is deficient in showing whether RSK family members also regulate cardiac fibrosis. In this study, the inventors now show a role for RSK3 in interstitial fibrosis that is independent of its function in hypertrophic signal transduction.

Hypertrophic cardiomyopathy (HCM) is the most commonly inherited heart defect (1 in 500 individuals) and the leading cause of sudden death in children, accounting for 36% of sudden deaths in young athletes (Maron 2013). HCM is caused by dominant mutations in sarcomeric proteins that typically induce myocyte hypertrophy and disarray and interstitial fibrosis. However, the phenotype and clinical course resulting from HCM mutations can vary such that genotype-positive patients without left ventricular hypertrophy can display myocardial fibrosis, diastolic dysfunction, and ECG abnormalities (Maron 2013). Studies using transgenic mice also indicate that the phenotype of HCM mutations depends upon genetic background (Prabhakar 2001, Michele 2002). As described below, expression of the HCM mutation Glu180Gly amino acid substitution of the thin filament protein α-tropomyosin (TM180) in mice of a mixed C57BL/6; FVB/N background results in a small left ventricle with interstitial fibrosis. The inventors show that RSK3 is required in this non-hypertrophic HCM model for the development of interstitial fibrosis and the signs of left-sided heart failure.

Methods

Supplemental Material

Reagents:

Primary antibodies included mouse 1F6 monoclonal anti-RSK3 (Abnova, cat# H00006196-M01) that detects all RSK family members (Spinale 2013), OR43 rabbit anti RSK3, and N-16 goat anti-RSK3 (Santa Cruz Biotechnology). Secondary antibodies included horseradish peroxidase (HRP)-conjugated donkey secondary antibodies (Jackson ImmunoResearch). RSK3 immunoprecipitation was performed as previously described (Spinale 2013).

Mice:

All experiments involving animals were approved by the Institutional Animal Care and Use Committee at the University of Miami. The RSK3^(−/−) C57BL/6 mouse was mated to the TM180 transgenic FVB/N mouse (Spinale 2013, Edgley 2012). All mice studied were littermates from RSK3^(−/+) X TM180; RSK3^(−/+) breedings, such that the background strain was 50:50 C57BL/6; FVB/N. All four genotypes were present in typical Mendelian proportion. Unless otherwise specifies, all experiments were performed with mice that were 16 weeks of age. Genotyping was performed at weaning by PCR using tail biopsy samples as previously described (Spinale 2013, Edgley 2012).

Echocardiography:

A Vevo 770TM High-Resolution In Vivo Imaging System (VisualSonics) with a RMVTM 707B “High Frame” Scan-head was used for imaging. Mice were anesthetized with 1.5% isoflurane for both B-mode and M-mode imaging.

Histochemistry:

Heart tissue was fixed in 3.7% formaldehyde. De-paraffinized 5 μm tissue sections were stained using the Picrosirius Red Stain Kit (Polysciences) and Alexa Fluor 555 Wheat Germ Agglutinin conjugate (Invitrogen) as recommended by the manufacturers. The cross-section area of >150 myocytes in >3 distinct regions of the left ventricle were measured per heart using the wheat germ agglutinin sections. Collagen content was assayed using the Picrosirius Red stained sections and linearly polarized light microscopy for >3 4× objective fields per heart. Note that while linearly polarized light microscopy is a highly specific assay for fibrillar collagen, the values obtained are an underestimate of total collagen content. TUNEL staining for both fixed cells and tissue sections was performed using the In Situ Cell Death Detection Kit, TMR red (Roche). Morphometrics and collagen content were measured using IPLab microscope software (BD Biosciences). All analyses were performed by a blinded investigator.

RNA Assay:

Total RNA was quantified with a Nanodrop 8000 Spectrophotometer (ThermoScientific) and quality controlled using with a Bioanalyzer 2100 and the RNA 6000 Nano kit (Agilent). The NanoString assay is based on direct, multiplexed measurement of gene expression without amplification, utilizing fluorescent molecular barcodes and single molecule imaging to identify and count multiple transcripts in a single reaction. Briefly, 100 ng total RNA were hybridized in solution to a target-specific codeset overnight at 65° C. The codeset contained dual, adjacently placed 50 bp oligonucleotide probes against the entire panel of genes, one set of probes fluorescently bar-coded and the other biotinylated. The hybridization reactions were loaded onto the NanoString Prep station which removes excess oligonucleotides and binds the hybridized mRNA to the Streptavidin-coated cartridge surface. The cartridges were loaded onto the NanoString Digital Analyzer, and 1150 fields of view were fluorescently scanned to count only those individual mRNAs bound to both a biotinylated and fluorescently bar-coded probe. Datasets for each RNA sample were normalized to internal positive controls and background-subtracted. Probe sequences are available upon request.

Statistics:

For all experiments, n refers to the number of individual mice. All data are expressed as mean±s.e.m. p-values were calculated using two-tailed Student's t-tests, paired or un-paired as appropriate, and are not corrected for multiple comparisons. Repeated symbols represent p-values of different orders of magnitude: * p<0.05, ** p<0.005, *** p<0.0005.

Results

FVB/N TM180 transgenic mice were crossed with C57BL/6 RSK3 knock-out mice such that all mice were of a mixed 50:50 background. RSK3 expression was slightly higher (˜25%, p=0.12) in the TM180 mice, while absent in RSK3^(−/−) mice, with no evidence of compensatory changes in the expression of other RSK family members (FIG. 32). Expression of the TM180 transgene was evident by the expected change in α-tropomyosin bands detected by total protein stain (Prabhakar 2001). In these mice of mixed lineage, the TM180 transgene induced a small heart phenotype that included a reduced biventricular weight (21%) and left ventricular myocytes with a proportionally smaller cross-section area (FIGS. 32 and 34). By echocardiography, the TM180 mice had reduced left ventricular internal dimensions, but increased contractility, i.e., both increased fractional shortening on M-mode and increased endocardial fractional area shortening on B-mode (FIGS. 31 and 36). That the changes in the TM180 left ventricle were pathologically important were implied by both an increased atrial weight and a significant, albeit small (12%) increase in wet lung weight, consistent with the presence of mild pulmonary edema and left-sided heart failure (FIGS. 32D and 34).

RSK3 knock-out had little effect on the heart in the absence of the TM180 transgene. While RSK3 knock-out did not reverse the small heart phenotype of the TM180 mouse nor prevent the atrial enlargement (FIGS. 32B,C and FIG. 34), the cardiac function of TM180; RSK3^(−/−) mice was more like wildtype mice, including a 29% lesser decrease in short axis dimension by echocardiography (FIGS. 31 and 36). Notably, the increase in fractional shortening and endocardial fractional area shortening due to the TM180 transgene were both attenuated by ˜50% by RSK knock-out. That the more “normal” cardiac function of the TM180; RSK3^(−/−) mice was physiologically important was implied by the observation that wet lung weight was no longer increased following RSK3 knock-out (FIG. 32D and FIG. 34).

There was no increase in cellular death associated with the TM180 transgene at 16 weeks of age (˜10⁻⁴ TUNEL-positive nuclei for all cohorts, data not shown). However, trichrome staining of the TM180 hearts revealed a patchy interstitial fibrosis in the myocardium not present in wildtype mice that was greatly reduced in the absence of RSK3 (FIG. 33A,B). Likewise, picrosirius red staining showed that fibrillar collagen content was increased by the TM180 transgene only in the presence of RSK3 (FIG. 33C). These results were corroborated by assay of the expression of genes involved in cardiac function and remodeling (FIG. 35). Notably, genes involved in cardiac fibrosis, including Col8a1 and Postn, (Oka 2007) encoding collagen type α1 and periostin, respectively, were induced by the TM180 transgene in a RSK3-dependent manner (FIG. 33D,E).

Discussion

When expressed in FVB/N mice, the HCM TM180 mutation results in concentric left ventricular hypertrophy, extensive fibrosis, atrial enlargement, and death within 5 months (Prabhakar 2001). In contrast, expression of the TM180 mutation in C57BL/6 mice resulted in no ventricular hypertrophy or fibrosis and a lower heart weight (Michele 2002). The inventors found that in a mixed C57BL/6; FVB/N background, the TM180 transgene induced an intermediate phenotype, including decreased ventricular and increased atrial weights, smaller ventricular myocytes, interstitial fibrosis, and increased contractility by echocardiography. The TM180 mutation is thought to induce cardiomyopathy as a result of the increased Ca²⁺ sensitivity and increased maximum tension generation of TM180 filaments (Prabhakar 2001). Hence, increasing Ca²⁺ reuptake through manipulation of phospholamban and the sarco/endoplasmic reticulum Ca²⁺-ATPase 2A (SERCA2A) can ameliorate the TM180 FVB/N phenotype (Gaffin 2011). The inventors have utilized the TM180 transgenic mouse to investigate the role of RSK3 in cardiac fibrosis. While the inventors and others have found that total heart ERK1/2 is activated in TM180 FVB/N mice (Gaffin 2011), in the mixed background mice, total ERK1/2 and RSK phosphorylation was not increased. Instead, the inventors only noted a slight increase in RSK3 protein levels (FIG. 32A). Importantly, RSK3 knock-out blocked the TM180 associated induction of fibrotic gene expression and interstitial fibrosis, as well as improving cardiac function both in terms of echocardiographic findings and wet lung weight. These findings complement our previous observation that RSK3 is specifically required for pathological cardiac hypertrophy. Without being bound by a particular theory, the inventors suggest that due to RSK3 anchoring through its unique N-terminal domain to scaffold proteins such as mAKAP (muscle A-kinase anchoring protein), RSK3 serves a unique function in the heart, despite the higher level of expression of other RSK isoenzymes (Li 2013). There are reports that RSK phosphorylation of CEBP/β is involved in pathological fibrosis of the liver and lung, but there is no published data relating to RSK family members in the heart. The inventors suggest that specific RSK3 inhibition should now be considered more broadly as a therapeutic target both in hypertrophic and fibrotic heart diseases.

Example 3 mAKAP Gene Structure and the Strategy for a Conditional mAKAP Allele

The mAKAP gene contains 12 common (light blue) and 3 alternatively-spliced exons (beige and yellow). A targeting vector containing negative (tk) and positive (neo) selectable markers was designed to conditionally delete the common Exon 9. The inventors obtained 6 targeted ES cell clones as shown by Southern blots. After breeding of targeted mice, the neo cassette was deleted by mating to a FLP recombinase transgenic. Mating to a mouse expressing cre recombinase will result in the deletion of Exon 9 (KO allele), producing a frame shift and introduction of a stop codon (red) in Exon 10. Mouse genotyping is being performed by PCR of genomic DNA with primers 44 and 45. (FIG. 37). For the western blot: mAKAP Ex9^(fl/fl); Tg(Myh6-cre/Esr1) mice (lanes 2 and 3) and mAKAP Ex9^(fl/fl) (lane 1) and Tg(Myh6-cre/Esr1) (lane 4) control mice were fed 500 mg tamoxifen/kg dry food for one week before the hearts were collected to prepare total RNA and protein extracts. RT-PCR was performed using primers located within mAKAP exons 4 and 11 which yield a 1022 bp for wildtype (and floxed) mRNA and a 901 bp product for a mAKAP mRNA species lacking exon 9. While control b-actin mRNA was similarly detected for all samples (bottom panel), >90% less PCR product was obtained for CKO mouse hearts (top panel, lanes 2 and 3) compared to that observed with the control hearts (lanes 1 and 4). Western blots were performed using VO54 mAKAP-specific antibody. No mAKAP protein was detectable for heart extracts prepared from CKO mice (lanes 2 and 3, top panel). Equal loading was determined by Ponceau total protein stain (bottom panel).

mAKAP Ex9^(fl/fl);

Tg(Myh6-cre/Esr1) mice (fl/fl; MCMTg) and Tg(Myh6-cre/Esr1) (MCM Tg) at 8 weeks of age were fed tamoxifen-containing chow for one week, rested for one week and then subjected for to 2 weeks of Transverse Aortic Constriction before analysis.

Transverse Aortic Constriction:

All tools were sterilized with a Germinator 500 Dry Sterilizer and Betadine Solution (10% povidone-iodine topical solution). Anesthesia was induced with 5% isoflurane and maintained with 2% isoflurane and 100% oxygen at a flow rate of 1.5 L/min using a SurgiVet flow regulator via nose cone. Loss of consciousness was verified by toe pinch. Mouse fur over the left chest and sternum was removed with a calcium hydroxide lotion (e.g. Nair), and the surgical site was sterilized with betadine. The skin was incised exposing the pectoralis muscle and the second left intercostal space. The pectoralis muscle and the second rib were blunt dissected and retracted revealing the thymus within the mediastinum. The lobes of the thymus were retracted to reveal the transverse aortic arch as well as the right innominate and left common carotid arteries. Blunt dissection though the connective tissue between these two arteries and under the aorta allowed for the passage of a 6-0 silk using a modified ligation aid (Fine Science Tools 18062-12). A 27 gauge needle was placed on top of the aorta and the 6-0 silk was tied around the needle. The needle was removed, leaving a constricted aorta. The chest was closed in two layers with 5-0 Polysorb Suture. Isoflurane administration was terminated, and the mice were maintained on 100% oxygen by nose cone until conscious. Immediately post-operatively, buprenorphrine (0.05-0.1 mg/kg s.c.) was administered and then q12 h prn. The mice were allowed to recover under a heat lamp until alert and active. Sham-operated mice that experience all but the placement of the aortic ligature served as controls.

Echocardiography:

Mice minimally anesthetized with 1-2% isoflurane were studied using a Vevo 770®, High-Resolution Imaging System (VisualSonics). The pressure gradient following TAC was calculated from the pulse wave Doppler velocity at the point of ligation as follows: P=4ν²; P=the induced pressure gradient (in mmHg) and ν=the velocity across the constriction (in m/s). (FIG. 39).

Example 4

RSK3 Anchoring is Important for Neonatal Rat Ventricular Myocyte Hypertrophy. FIG. 40.

A. mAKAPβ complexes were immunoprecipitated using FL100 mAKAP antiserum from PE-treated, adenovirus-infected myocytes expressing myc-GFP or myc-GFP-RBD (mAKAP 1694-1833) and detected with the pan-RSK 1F6 and mAKAP 211 antibodies. B. Transfected myocytes expressing GFP or GFP-RBD (green) were stained with α-actinin (blue) and ANF (red) antibodies. Bar=20 μm. C. Cross-section area of myocytes. n=5. D. Fraction of myocytes expressing ANF. n=3. * p-values comparing to GFP-expressing samples. †p-values comparing to no agonist control. E and F. Same as C and D except for myocytes expressing GFP or HA-tagged RSK3 1-42.

Neonatal Rat Myocytes Isolation and Culture:

1-3 day old Sprague-Dawley rats were decapitated and the excised hearts placed in 1×ADS Buffer (116 mmol/L NaCl, 20 mmol/L HEPES, 1 mmol/L NaH₂PO₄, 5.5 mmol/L glucose, 5.4 mmol/L KCl, 0.8 mmol/L MgSO₄, pH 7.35). The atria were carefully removed and the blood washed away. The ventricles were minced and incubated with 15 mL 1×ADS Buffer containing 3.3 mg type II collagenase (Worthington, 230 U/mg) and 9 mg Pancreatin (Sigma) at 37° C. while shaking at 80 RPM. After 15 minutes, the dissociated cardiac myocytes were separated by centrifugation at 50×g for 1 minute, resuspended in 4 mL horse serum and incubated 37° C. with occasional agitation. The steps for enzymatic digestion and isolation of myocytes were repeated 10-12 times to maximize yield. The myocytes were pooled and spun down again at 50×g for 2 minutes and resuspended in Maintenance Medium (DMEM:M199, 4:1) supplemented with 10% horse serum and 5% fetal bovine serum. To remove any contaminating fibroblasts, the cells were pre-plated for 1 hour before plating on gelatin-coated tissue culture plasticware. This procedure yields >90% pure cardiac myocytes. After 1 day in culture, the media was changed to maintenance medium containing 0.1 mmol/L bromodeoxyuridine to suppress fibroblast growth.

Experiments were initiated 1 day after myocyte isolation. Adenoviral infection was performed by addition of adenovirus (multiplicity of infection=5-50) to the media. Plasmids and siRNA oligonucleotides were transfected using Transfast (Promega) and Dharmafect (Thermofisher), respectively, as recommended by the manufacturers using cells cultured in maintenance medium supplemented with 4% horse serum. Starting the day after gene transduction, the cells were treated for as long as 2 days, as indicated for each experiment.

Immunocytochemistry:

Cultured neonatal cardiomyocytes on plastic coverslips were fixed in 3.7% formaldehyde in PBS, permeabilized with 0.3% Triton X-100 in PBS, and blocked with PBS containing 0.2% BSA and 1% horse serum for 1 hour. The slides were then sequentially incubated for 1 hour with primary and Alexa fluorescent dye-conjugated specific-secondary antibodies (Invitrogen, 1:1000) diluted in blocking buffer. The slips were washed three times with blocking buffer. 1 μg/mL Hoechst 33258 was included in the last wash stop to label nuclei. Slides were sealed in SlowFade Gold antifade buffer (Invitrogen) for fluorescent microscopy. Wide-field images were acquired using a Leica DMI 6000 Microscope.

AAV9 containing the indicated CIS plasmid encoding myc-GFP-mAKAP 1694-1833 were injected into neonatal wildtype mice. 2 week TAC was performed and analyzed as above at 8 weeks of age. (FIGS. 41-42).

The patent and scientific literature referred to herein establishes the knowledge that is available to those with skill in the art. All United States patents and published or unpublished United States patent applications cited herein are incorporated by reference. All published foreign patents and patent applications cited herein are hereby incorporated by reference. All other published references, documents, manuscripts and scientific literature cited herein are hereby incorporated by reference.

While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.

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1. A method of protecting the heart from damage, by administering to a patient at risk of such damage, a pharmaceutically effective amount of a composition which inhibits the interaction of RSK3 and mAKAPβ.
 2. The method of claim 1, wherein the composition is a RSK3 peptide.
 3. The method of claim 2, wherein the RSK3 peptide is obtained from the amino terminus of the RSK3 amino acid sequence.
 4. The method of claim 3, wherein the RSK3 peptide is amino acids 1-42 of the RSK3 amino acid sequence.
 5. The method of claim 2, wherein the polypeptide is administered directly.
 6. The method of claim 2, wherein the polypeptide is administered using a viral vector.
 7. The method of claim 6, wherein the vector is adeno-associated virus (AAV).
 8. The method of claim 1, wherein the composition is a small interfering RNA (siRNA) that inhibits the expression of RSK3.
 9. A method of treating heart disease, by administering to a patient a pharmaceutically effective amount of a composition which inhibits the interaction of RSK3 and mAKAPβ.
 10. The method of claim 9, wherein the composition is a RSK3 peptide.
 11. The method of claim 10, wherein the RSK3 peptide is obtained from the amino terminus of the RSK3 amino acid sequence.
 12. The method of claim 11, wherein the RSK3 peptide is amino acids 1-42 of the RSK3 amino acid sequence.
 13. The method of claim 9, wherein the polypeptide is administered directly.
 14. The method of claim 9, wherein the polypeptide is administered using a viral vector.
 15. The method of claim 14, wherein the vector is adeno-associated virus (AAV).
 16. The method of claim 19, wherein the composition is a small interfering RNA (siRNA) that inhibits the expression of RSK3.
 17. A composition comprising a molecule which inhibits the interaction of RSK3 and mAKAPβ.
 18. The composition of claim 17, wherein the molecule is a peptide.
 19. The composition of claim 18, wherein the molecule is a RSK3 peptide.
 20. The composition of claim 19, wherein the RSK3 peptide is obtained from the amino terminus of the RSK3 amino acid sequence.
 21. The composition of claim 20, wherein the RSK3 peptide is amino acids 1-42 of the RSK3 amino acid sequence.
 22. The composition of claim 17, wherein the molecule is expressed using a viral vector.
 23. The composition of claim 22, wherein the vector is adeno-associated virus (AAV).
 24. The composition of claim 17, wherein the molecule is a small molecule.
 25. A method of treating or preventing heart disease, by administering to a patient a pharmaceutically effective amount of a composition which inhibits the activity of RSK3.
 26. The composition of claim 25, wherein the small molecule is SL0101 or BI-D1870.
 27. A method of treating or preventing heart disease, by administering to a patient a pharmaceutically effective amount of a composition which inhibits the activity of mAKAPβ.
 28. The method of claim 27, wherein the composition is a mAKAPβ peptide.
 29. The composition of claim 28, wherein the mAKAPβ peptide is amino acids 1694-1833 of the mAKAPβ amino acid sequence.
 30. The composition of claim 28, wherein the mAKAPβ peptide is amino acids 1735-1833 of the mAKAPβ amino acid sequence.
 31. The composition of claim 27, wherein the molecule is expressed using a viral vector.
 32. The composition of claim 31, wherein the vector is adeno-associated virus (AAV). 